No USB cams are ever going to be that great really.. As they use compression to squeeze everything through USB. I have a USB Kritter, which is ok and comes with good software. But they are over priced... For half the money I then bought a Philips Vesta, which is better quality all round. And has a built in mic. Not so good software tho. But then software like iVisit (ivisit.com) is free from the net anyway. I am told the 3com cams are good too, although i've not tried them.
If you have a FireWire equiped Mac, then FireWire web cams are now available too for not that much more money than a good USB cam. Quaility should be MUCH better.