I've used 4 different webcams over the last 7 years or so
The LogiTech pro4000 was by far the worst much to my disapointment, I resold it after 3 days of playing with its settings.
The best I've used is a plain ol' camcorder, I got one for something else and was happily surprised that it doubles as a webcam! its a Sony TRV250. Its a digital 8 recorder and SUPER easy to transfer any type of home video to a PC via USB or firewire. Used you can get it for 85$ new they are about 200$ish. I can't imagine a better picture.
The second best I've used is the 3com HomeConnect, its a bit older (maybe '97) and by no means is it perfect, but it does a good job with colors and various lighting environments, and far exceeded the LogiTech. (they dont come with XP drivers but you can download them online, you can buy this cam used for about 30$ or new for about 60$ - ebay)
if you want to see various webcams and ask people what they are using then I highly recommend you download a version of ICUII (.com) its software for peeps that have webcams and can be kinda cool!