You mean something that emphasizes the long head?
When I target a muscle, I want something that nails the entire thing. I feel that trying to zero in on small portions is a waste of gas, time better spent just trying to get bigger. Chances are good that if you're doing "fundamental" triceps exercises and your long heads aren't where you'd like 'em, you just need bigger triceps overall anyway.
There's a lot of debate over what triceps exercise is best. I like parallel dips. A lot of people swear by close-grip bench press. Others, like Doggcrapp, really like Barbarian-style bench pressing with a close grip.
There are still plenty of quality movements to choose from after those--overhead extensions definitely changed my triceps for the better--but as a rule of thumb, I've found that an exercise with decent range of motion that allows for a *lot* of weight to be moved is going to do a superior job. I qualify this with the full ROM because there are lots of exercises that let you use some heavy poundages, like decline presses, but aren't ideal because people usually do them with such a short ROM. (Decline presses to the neck kick ass, though.)
There are a few exceptions, and we all have our favorites so occassionally we'll deviate from this "rule," but stick to heavy dips, close-grips, and Barbarian benches, and your triceps will have to grow, all other conditions being favorable.