Deviantart is probably the most well-known. It's technically also the most well-known for art thieves, so I recommend watermarking your work.

Furaffinity and weasyl are a couple other ones I know of, but I'm not too familiar with the community there.

Toyhou.se is a good website for selling OCs, adoptables, and such.

There are other websites that are also good for comms/adoptables/etc, but they fall outside of what I can discuss on Wolfplay.