I think it's good to switch up your exercises anyway. Some other good triceps exercises would include skull crushers (laying triceps extensions), standing triceps extensions, parallel bar dips, bench dips (reverse pushups), and strict dumbbell kickbacks.
I think you have to be pretty strict with any exercise where you're specifically targeting the triceps, if the exercise calls for it. It's easy to get sloppy on any exercise; forgetting what your purpose is, or getting carried away with how much weight you're shooting for. Kickbacks for instance, although highly criticized by many people, have proven a quality triceps isolation exercise for me, because I concentrate so much on my form. Rather than swinging the arm to lift the weight, the top of my arm hardly wavers from parallel, since I'm using my triceps alone to lift the weight (although I'm pretty sure my deltoids are contracting for stabilization).
I don't think kickbacks should be the staple exercise of your triceps program, however. I like to start out with close-grip presses or parallel bar dips, then move to some extensions, and finish off with kickbacks or pressdowns.
Just switch it up, go as heavy as you can, while maintaining strict form, contract your triceps at the peak of the movements and flex them between sets. You should see some good results, even without close-grip presses. Happy training!