A couple of months back, I picked up the Logitech C270 for skype. I didn't want to spend a lot of money on a webcam, and I figured for $30, this little 720p USB webcam would probably suffice. I got a lot more for my money than I thought I would.
While the video quality on this webcam certainly isn't spectacular, it definitely exceeded my expectations for the price I paid.
The quality of the microphone in this little webcam is absolutely astounding. Before I picked up this little unit, I was using a $15 dollar desktop microphone by Audio Technica (which, by the way, I recommend everyone avoid like the plague.) I assumed that the quality of the microphone in this webcam would be worse than that of the AT desktop mic, but Skype auto-configured itself to use the built in webcam mic. In the Skype test call, I was astonished at how clear the audio was compared to the previous microphone. It's by far the best microphone I've ever used (out of a handful of headsets, desktop microphones, built in microphones, etc.) and the quality you get for the price point is ridiculous. Friends of mine that have "high end" gaming headsets were astonished at the quality of the microphone (quality that blew their headset's mic out of the water) and didn't believe me when I told them it was a webcam mic. It was easy to configure the mic to be used in games, and I haven't touched my other mic since.
If you're looking for an affordable webcam with decent video quality and excellent sound quality, consider taking a look at Logitech's offerings. Mine was on the cheaper end of the spectrum, so I'd be interested to see how their more expensive lines compare.