ArcheAge. Has lots of guilds with 300+ members, several fansites (with Archeagesource being the biggest/best), and active sub-reddit, etc.. Bad thing is, it's now IP blocked on the Russian version, which is the most active for international players. You'll have to use a VPN to play now, I believe. If you made an account before the IP Block, however, you wont need a VPN. There's also a Chinese, Korean and Japanese version you can give a go. NA/EU should be out, at least in beta, within the next few months.
I also second GW2.