Tips:
1. Lighting: webcam image quality is enhanced almost 10 fold by lighting your scene. I don't mean just slap a spotlight on the subject, but nice AMBIENT lighting seems to work best.
2. Compression: Compressing the video is sometimes done on-the-fly. But if your stuff is huge in size AND blury, it may be a cack webcam
As for purchasing, we've just done several installations for clients who wanted 'Live-Cams' on the premises for streaming to their website.
Here's some observations:
1: Cost does NOT equal quality
2: USB2 is practiacally essential. Check the cam is USB2, and make sure your machine accepts USB2
3: Software wasn't an issue for us, as we were using custom software, but getting a cam with a decent brand name will mean longevity support for drivers, and usually a nice software bundle
3: If its' REALLY bad, send it back: We bought 5 identical cams. One of them had APPALLING quality. It was sent back and replaced, no quibble. If however that one cam had been the one we bought, and the ONLY one, we'd have probably never known how good the actual quality was
OK, heres' some I would recommend (at home, and at work, I use an Apple iSight, which is Firewire, and pretty much creme-de-la-creme, but we HAVE been buying others, so I know of what I speak

)
1. Logictech QuickCam Sphere V3 (£63 approx)
http://www.scan.co.uk/Products/ProductI ... tID=101340
2. Creative Live Motion (£69 approx)
http://www.scan.co.uk/Products/ProductI ... tID=282304
These cameras offer top quality for video recording at your desktop. 640x480 pixels at 30fps put on your TV screen is pretty much VHS quality.
We have installed both for clients, and not heard a bad word about either of them.