I saw this as a search to my site here, so I felt like I’d answer this question, in case this search was done again recently. Wyrmrest Accord and Moon Guard are, in my opinion, the top two for RP in WoW. However, if you’re on Moon Guard, and you play alliance…. Stay away from Goldshire…. Just…. trust me.
Wyrmrest Accord is a bit more organized with the RP, while Moon Guard is more clique based. There are clique groups on both sides, but a few people from WRA got together and made a site, Wyrmrest Accord.net, and have a lot of organization and open discussion on RP. There’s even an in-game chat channel wranet for the people registered with this site.
There’s also Steamwheedle Cartel, which is an RP-PvP server. It used to be good with RP, and I’ve heard some chatter that it’s making a come-back, but it’s also a PvP server, which means that no matter what, you’re flagged in the Barrens, you’re flagged in contested territories, just like all the new content zones added since BC, so be prepared for people just coming up on you and ganking you cause they feel like it while you’re questing. That’s the reason I stay away from PvP servers. I’d like to be in control of when I decide to PvP. Call me a carebear if you wish, you can even call me Trueheart.