Diet, low rep-high weight and walking the treadmil on a rather steep incline should get you an ass.
The exercises:
Dead Lifts
Hip... Thingies (forgot the name), it's that machine that has two handles you stand between, and this big lever you roll clockwise and CC. Damn my English is bad, so is my ascii art, but still a go:
|.........|
|....o...|
|.../.....|
|.O......|
|.........|
|.........|
You stand between those lines (they represent the bars), hold the bars, put your leg on the cushion (the capital O), keep it streight and kick backwards. Anyone know how it's called?
Then you might wanna add curls, hyper extenstions (I am not talking about knee extentions, but on the lower back long muscles), I don't know what a squat is, I think it's that think where you hold a free weight on your shoulders, stand streight and then go down while keeping the back up and streight, the knee caps pointing forward and the heels all stuck to the ground, it works great on your higher front hip (or do they call that thighs? BAH!).
If we are talking about the same thing, it's also good for the ass, you would want to go all the way down, otherwise, you only train the lower part of the muscle, and that's a whole way down from your ass.
The best routine is if you do over all training, I never like focusing on one thing only. Trust me, your body is better off without focusing and it will fix any problem you might have even if you don't just focus on that one...
Good Luck anyway!