I guess it depends on where you are progression- and gear- wise, but the BoP engineering goggles are pretty sweet. Mining air clouds is also very fun and can be quite profitable if the primal air prices haven't already tanked on your server due to everyone else doing it. Half an hour in Nagrand can net you a good chunk of change after you tally up the ore & Primal Air you end up with.
Also, Gyrocopters.:)
EDIT: I should say though, if I were you at this point in the game, I would probably stay with Leatherworking just because you KNOW the expansion is going to add some insane BoP set that's perfectly itemized, just like with Tailoring & FSW. At the very least I would wait until more info about WotLK professions comes out and make a decision then. It'd suck to have to grind out Leatherworking again.
Also, Gyrocopters.:)
EDIT: I should say though, if I were you at this point in the game, I would probably stay with Leatherworking just because you KNOW the expansion is going to add some insane BoP set that's perfectly itemized, just like with Tailoring & FSW. At the very least I would wait until more info about WotLK professions comes out and make a decision then. It'd suck to have to grind out Leatherworking again.