Reverse Grip Skull Crushers
This is an excellent variation on a very popular tricep exercise.
Switching the grips on your tricep exercises puts a different emphasis on each of the three heads (that's why they are called TRIceps) of the muscle.
I like this variation because it also adds in a level of Grip strength. It's a bit scarier because of the lack of limbs between your face and the bar, so don't go ham on this lift until you've got some experience with it!