Are you doing any cardio too? (Treadmill, elliptical, etc.) Doing cardio might help tighten them up a bit. (And since they use slow-twitch muscles, they don't bulk like the fast-twitch muscles used in weights/lunges/etc.)
Also, make sure you're going through the full movement of the lunge/work. If you're stopping too short or don't have good form, you're only working part of the muscle, instead of the whole thing, and this will cause it to bulk up in one section instead of being "long and lean."
Try mixing up your exercises too, so that it's not all lunges.
--Janis