I had a bit of bad luck while shopping around for my webcam to use w/ my G4 iBook. Some of the USB cams are ok (so I've read) but for some you have to install third party software to get it to run properly, and I wasn't very keen on that, especially when the software cost ten bucks. So, I bought the iSight and it works great, no problems at all.
Apple recommends for the iSight:
System Requirements:
Macintosh computer with a 600MHz or faster PowerPC G3 or any PowerPC G4 or G5 processor
iChat AV software (Included with Mac OS X Panther)
Mac OS X v10.3 or later
Broadband Internet connection (128Kbps or faster transfer speeds)
Considering that you've got a G3, a good amount of ram and OS X 10.4, I would say that you could go with the iSight. From what I have read, the quality of the iSight can't be beat. And it works seamlessly with iChat and Skype, which is excellent.
Check out eBay or the
Marketplace forum here on MacNN (that's where I got mine).
As for wireless webcams, can't help you there. I have no idea. And there's only one model of the iSight. Hope this helps!