I bought the @adafruit USB Digital microscope http://www.adafruit.com/products/636 for $80. After some initial fumbling (ignore the enclosed CD and download the drivers/software from Adafruit...oh, and RTFM), it works great...especially for the price.

Here are some screen shots at both 20x and 200x.

(download)

Click here to download:

first-impressions-of-usb-microscope-from-adafruit-JhtGFxlkABdpFnifkJDh.zip (4.64 MB)

The Windows software has all the advanced features, but the Mac program works fine if you just need to get a quick shot or video. Bio geeks will want the Windows version to do time-lapse recording, etc. The stand provided is of minimal usefulness for practical puposes...an obvious project is to fashion a mount for a microphone stand or lamp swing-arm. Focus adjustment can be a bit tricky as the adjustment is somewhat stiff, and so is a little hard to make the fine adjustments without accidentally repositioning the camera. Nits, really. For the price you can't beat it.