Like Mel indicated, there are lots of different exercises that will help prevent or get rid of those "bat wings". If the problem is that you just can't see your triceps, then it is a matter of losing a couple of more pounds.
I would focus on a basic pressing exercise and work on getting as strong as possible. Overhead press or benchpress with either a barbell or dumbells is where I would start. If you can work up to bodyweight on the benchpress or 2/3 BWT on the OHP I guarantee your triceps will be toned.
If you really want to focus on tricep isolation work for "esthetic' reasons, or to help your press, I like these dumbell extentions : Tate Press
They work best with hex dumbells, and you need to start really light. I was using 50# Dumbells for sets of 12 when I was bench pressing 360#.