The first social step anyone has in WoW is your Guild. We've talked about how it can form the core of your player experience, for good and bad. But, not everyone's lucky enough to have a Guild ready-to-go at everything you might want to do, and what's more, ready at a moment's notice. Many Guilds (rightly so) will expect each members to show some individual initiative, and maybe brave at least a few PUGs. Well, a pair of tools have popped up recently to help you get set up with people outside the limited scope of your Guild.
As a caveat: Both sites I'm presenting here are relatively new and untried. You're getting in on a ground floor, but we can't promise fame and fortune from them (yet).