These 3 are the ones I know that are free to watch.
1. Chaturbate
2. MyFreeCams
3. Cam4
There are a tons more, but for most of them you need to pay credits, before seeing any of the action. You can also check the webcam category on theporndude. They list the best ones.
Chaturbate is the best one currently in my opinion, so check that one out ;)