Total newbie - What to purchase for Raspberry Pi home theatre?

I already am doing something that sounds like just want you want to do.  I have a Raspberry Pi connected to our 50inch Samsung TV using the HDMI input. 

Parts I'm using:

Raspberry Pi

A two amp, two port USB power brick I got at the local Home Depot (I chose this because it allows 1 amp at 5 volts for each USB socket)

HDMI cable (whatever length you need - mine is 3 feet long)

USB to micro USB cable for power (whatever length you need - mine is 3 feet long)

Mouse/keyboard combination: I am using the "Logitech MK260 Wireless Desktop Model: 920-002950 | Radio Shack Catalog #: 26-1553" that I bought from my local Radio Shack store for $29.99 (US$).  I like it because the mouse and keyboard both run off the same USB dongle, leaving the RPi's second USB port available.

Ethernet: Mine is cabled (I finally ran an Ethernet cable thru my attic to the wall behind the TV), but before that I used a Wi-Fi USB dongle of a type with a tall antenna.

Mine is an "OURLINK WU335EC 300Mbps WIFI USB Adapter 802.11n Wireless PC laptop WIFI Network receiver transmitter" and I see one available at Amazon.com right now, but if it's gone, you can check Aliexpress.com to order one.  My wireless router is at the opposite corner of our house from the room with the TV and ONLY the tall wi-fi dongle got a good signal.  The newer RPi (revision 2) can run both those USB dongles at the same time without any problem.

For running XBMC, I tried all three of the popular distros with it: RaspBMC, OpenElec, and Xbian.  I had the easiest setup and fewest problems with RaspBMC (translation: I got frustrated messing with the others and RaspBMC just worked best for me.)  I'm sure other people got the other distros to work, maybe, but RaspBMC had what I needed.  NOTE: RaspBMC if you are using Wi-Fi:  You WILL want to first configure it while cabled to your Ethernet so that you can add the programs: "Network Manager" and "XBMC Backup".  The Network Manager will allow you to easily configure your wi-fi connection (to enter your router's SSID and password).  The XBMC backup will soon reveal its usefulness after you've selected a few video channels you like to watch.   You can use it to backup your RaspBMC settings to a USB flash drive (I used a USB hub to connect when I needed more than 2 USB things) and restore the settings if they get messed up, or if you make another RaspBMC card fresh and just want to pop the settings all done onto it.  You will see that in RaspBMC, there will ALREADY be a program called "RaspBMC Settings".  THIS was the magic bit that made it easier for me to use RaspBMC than the other two XBMC distros.  I was able to plug in the video and audio decoder keys I'd purchased, using that menu, and also mess with other settings like timezone, etc.

Here's a Skydrive link to some photos of my setup (taken before I had the wired ethernet in the living room): sdrv.ms/13Kf2hU (with the usual http colon slash slash prefixed in front of the sdrv.ms)

You can see the mini-USB hub in one of the photos, showing the Wi-Fi dongle at left, the mouse/keyboard dongle at right, and the (glowing) USB flash drive center/front.  I not only used the flash drive for RaspBMC backups, but it also had folders with photos and mpeg movies on it that I could watch using XBMC.

Have fun! - Oh!, the SD cards I'm using for most of my things are RiDATA 16GB, Class 10 cards that I bought online cheaper than many other brands and all of mine have worked just fine.

p.s. - all the videos and audio I'd played worked just fine before I bought the decoder licenses, too.

Thanks John for the detailed reply.  For the power supply, can I use an old cell phone charger and that has micro USB?  Or does it have to meet those specific requirements? 

Old cell phone charger:  If it says its output is 5volts and at least 500ma, it should work for most things you might do with your RPi.  If it says 700-750ma, it should work with all of them.  If it says 1000ma or 1amp at 5volts, you should not have any problems with it.  But there are many other power sources available to you.  Read on:

Power supplies - I've successfully used a wide range of power sources for my RPi projects.  What you really want to know is the current they allow.  500ma has worked for me for running headless RPi's with no USB devices and only the Ethernet attached and no display.  I've had absolutely no power problems with any power source on a RPi with such low power usage.  On a loaded up RPi, say with a Wi-Fi USB dongle and a wireless USB keyboard/mouse dongle, and an HDMI display connected, I believe some people have reported power drain up to 700-750ma.  Using a 1amp, 5volt power supply, you should not have any trouble running your RPi's. 

I have used the power supplies for my Creative Zen V+ and my Creative Zen Vision W, choosing the ones with the mini-USB connector and adding my own mini-USB to micro-USB adapter. I have two Creative Zen Vision W's and 4 Creative Zen V+'s so I had lots of spare power supplies for them.  I can buy more online as entire kits that also include both 115volt AC and 12volt car adapters, cheaper than some places sell a single power supply for the RPi.  I do still have to add the mini-to-micro USB adapter when using those, though.  I have also used a Belkin 3 outlet adapter that included 2 USB power sockets, also a Belkin power strip with cord that also had two built-in USB power sockets.  I don't even know for sure what those sockets are rated, but they seemed to have been working fine for all the RPi's I've run from them.  I ordered a cheap batch of 3 foot and 6 foot USB to micro-USB cords from some online store in eBay and saved a bunch of money and the hassle of always looking around for "where did I set that cord down last?"

But there may be other considerations:

Many newer TV's also have USB power sockets built-in, and most may only be rated 500ma but might still work for you.  My Samsung 50inch TV has both 500ma and 1amp USB sockets, labeled as such, and when I chose to use them, I used the 1amp socket for the RPi just to play safe.  BUT...!  If the USB socket on the TV turns off when the TV turns off, beware!  You will want to command the RPi to be powered down BEFORE you turn off the TV or you might corrupt your SD card image!  After a while, I decided it wasn't worth the hassle of remembering and I so now my Belkin power strip with the two USB sockets is behind the entertainment center and is used for powering the RPi's among other things back there.  I no longer power the RPi's from a TV USB port except when I'm at a PC club meeting running it from the back of my 19inch display and just trying to reduce the number of outlets needed.

Happily, unlike the iPad, iPod, whatever devices, the RPi does not care what is on the data lines of the power supply and can use the idevices power supplies as well.  The reverse is maybe not true.  I don't have any Apple devices, but I understand that they require certain resistances on the data lines to tell them to charge from the adapters.  Simple USB power supplies won't charge Apple devices correctly in many cases.  Of course this is by design so Apple can sell more of their power supplies.  But if you do happen to have an iPad AC adapter power brick, it WILL work with the RPi if you also have the USB to micro-USB power cord needed.  I'm pretty sure the iPad power bricks supply 1amp.

So you see you have LOTS of choices, many of which you can simply pick up at the local hardware store (the Belkin power strips and adapters with USB sockets).  Check the ratings and if they say 1amp, 5volt per socket or have 2 sockets and say 2amp USB power, you'll be fine.  eBay has lots of cheap sources for the USB to micro-USB power cords and while they take several weeks to be delivered (coming from Szenchen, China), they often cost under $2 per cable and have free shipping.  If you don't mind waiting for them to arrive, you can save a bundle.  I also got myself lots of cheap HDMI cables that way and find that even the cheapest HDMI cables seem to work just fine.  At least I haven't had any problems with mine.  Ditto for when I bought a 10-pack of assorted colors of 3 foot Ethernet cables for less than the cost of a single such cable at the local brick and mortar famous name electronics store.

Last word: If you plan on using heavy drain power devices on the USB ports of any RPi, I'd advise using an independently powered USB hub.  The dongle and flash drive things work just fine, but a USB hard drive or floppy drive or DVD player, with its internal motors, would draw way too much current for the RPi.  And if you plan on doing GPIO projects, be very careful to heed warnings about using any 5volt things connected to the GPIO headers.  The GPIO power supply pins are only intended for 3.3v devices, though some few things like the 16x2 LCD display can be used with it if directions are followed carefully.

You can NOT learn too much about power supplies and power specifications for GPIO projects with the RPi.  Keep reading and have fun with your projects.

p.s. - commands to shutdown and power off your RPi without messing up your SD card image:

#1 - from SSH or from the text console or terminal window, I use the command line:

sudo shutdown -h -P -t 3 now

#2 - from RaspBMC, click the power icon and select the second choice to "Power off system"

#3 - from Wheezy, configured to automatically start the desktop on boot, your power icon will provide the option to "Shutdown" and not just Logout or Exit.  Use Shutdown to power off your RPi.

In all examples, make sure you WAIT until ALL the LED's in the RPi go out except for the red one labeled PWR.  Especially wait until the first LED (labeled ACT), has completely quit blinking.

Power demands and overclocking!!!  I have NOT tried overclocking my RPi beyond the "Modest" (800mhz) option in the raspi-config menu. All the higher choices mention "over voltage" and I'm not yet ready to test a RPi to possible destruction.  At least not until I've added cooling fins on the 3 main chips and rigged a carefully regulated customized power supply.  Besides, anything over 5 volts and you void your warranty if you fry the RPi.  I have more patience to wait the few extra moments it takes the RPi to do something, than I do to wait the few weeks to get another.  Besides, once I get my RPi booted up and busy doing the task at hand, it seems that all my RPi's are running quite fast enough.  The mahjongg game I installed (sudo apt-get install mahjongg) plays just fine. The Calibre ebook reader (sudo apt-get install calibre-bin) is very slow loading, but once I have chosen an ebook to view and am reading it, that also works just fine.  The SD card I have configured with RaspBMC, once loaded and playing some video or other, is also running quite well.  These little computers were NOT built to use as race cars.  For that matter, I think you'll find that even formula one race cars have very short life expectancy for their engines, which are all really just severely overclocked internal combustion engines.  They burn brightly for a short time.  I want my RPi's to last a long time.  (oh, LOL!  I just had a flash vision of someone rigging an RPi on their RC race car!!  hahahahaha - yes, that's been done, I'm sure)

Thanks a bunch, you're a great help!

Thanks a bunch, you're a great help!