WoW uses TCP the last time I checked (the overhead of TCP is acceptable for an RPG in most cases). I believe Diablo 3 also uses TCP and uses protobuf.
EVE online have some very good tech posts and are generally quite open about their technology (although it's mostly about hardware and infrastructure). Valve also have some good articles on networking for Source games (someone posted the link elsewhere in this thread).
EVE online have some very good tech posts and are generally quite open about their technology (although it's mostly about hardware and infrastructure). Valve also have some good articles on networking for Source games (someone posted the link elsewhere in this thread).