Hi there, it's great you're looking for some effective, time-efficient exercises. I am very biased so please take this with a grain of salt, but I LOVE LOVE LOVE barre exercises for any part of the body but particularly the lower body (butt, thighs, glutes, and abs). Check out some DVD's or things you can download or watch on youtube. My personal favorites are Core Fusion, Pure Barre, and Kathy Smith, and they can be done by people of different fitness levels - there are tons out there. Or hire a trainer for a one-time session to design a program you can do on your own if regular training sessions are not feasible.
Good luck, and please keep us posted,