I recently got a Bresser BioLux NV microscope. Of course it is quite cheap and you get what you pay for. I'm still very pleased with it because it is a fun toy, and I'm not afraid to destroy something by not treating it properly. I'm also happy that the cam works well with Linux.
The cam only has a VGA 640×480 resolution but for me that's sufficient. It is recognized by my old Ubuntu 10.10:
Bus 002 Device 004: ID 18ec:3366 Arkmicro Technologies Inc
It looks like there is a very similar model with a different cam.
So far I use Cheese to look at my objects of interest (the two programs i found so far seem not to be intended for my purpose; http://gxsm.sourceforge.net/, http://valelab.ucsf.edu/~MM/MMwiki/index.php/Micro-Manager).