Mania's got an excellent, if longer-than-usual post up about an issue I'm dealing with as well: the need to play, but confusion about just what to do in the game. I've pretty much done everything I want to do on my Hunter -- after a very lucky night the other week, I'm decked out in all the gear I want, I've topped off my professions, and while I do have some reps to grind out yet (I still want a few rep mounts), most everything I want just depends on dailies, and those I can finish in just a few minutes a day. But just like Mania I've still got that itch to play, to explore and advance and progress, with nowhere to go.
For Mania, the answer turned out to be going to a Death Knight -- she may discover that she's opened up a whole new world in choosing to level with a completely different class. An alt was also the answer for me, but I have a few different reasons, the first of which is Engineering -- I thought for a while, after hitting 450 Leatherworking on my (also Skinning) Hunter that I would switch to Engie and just buy all the mats, but I think it'll be more fun (and profitable) leveling up a Mining/Engineering alt. And he can always make the BoE chopper for any of my characters as well.
But while an alt is sometimes the answer, there are lots of things you can dive into to find a completely new area in the game -- try Arenas for the first time, do a Wintergrasp grind, seek out an old world reputation or title that you've always wanted. We're very lucky, in a game like this, to have lots and lots of new things to try even when it seems like we've done everything we want.