The most recent edition of T-Nation's Exercises You've Never Tried series (#18) encouraged me to re-read the earlier articles in search of lost gems. Amongst them I found this treat - the Anconeus Sidekick - which soon formed part of an ever-growing Triceps-blasting arsenal.
The Anconeus is the oft-forgotten 4th elbow extensor. To perform the sidekicks, kneel down beside a bench and use it to support your upper arm. Move your upper arm so that it's at right angles to your torso (and parallel to the floor), with your forearm hanging straight down. Pick up a dumbell with a pronated grip (point your thumb down), and raise your forearm to horizontal (your upper arm won't move).
Follow it up with your usual tricep work.