The most important thing u can do is cardio and diet ( which im sure your doing), as far as excercises go:
* You can either hang from a fixed bar and pull your legs up to form a 90 degree angle with your lower back ( you can do 2 variations... your knees bent and your knees straight)
*you can do a similar thing with a dip machine ( or if your gym has a specific machine for this, i know my gym does)..its basically a dip machine ( no weights though), but they have paddings and a handle on the paraller bars so you can perform the "Leg-Ups" on those machine
*yo can hold a 45 plate in either hand, lets say your right hand... then put your left hand on your left ear, and bend sideways to your right ( same direction as the hand you have the weight in)... you can feel your obliques get a very good workout from that, it will also develope the sides of your lower abs..
* Romain chairs are also very good