I've seen the cheap USB type microscopes that can be hooked up to a PC but I'd want one that could be used in the workshop without the need for an attached PC.
Here's my feature list:
Big screen, perhaps an old desktop LCD?
On-screen grid or some method for measurement would be a useful feature
Snapshotting of images to SD (or some other storage)
The "camera" end would need to be small so I could poke it into things but also have tripod mount so could be fixed.