What're some exercises that will bulk up my triceps?

Compound exercises: The best exercises tend to be compound exercises (biceps curls and triceps extensions). These target multiple muscle groups yielding the greatest muscle hypertrophy.

Triceps bulk: Heavier exercises for triceps size include close-grip bench presses, overhead dumbbell extensions (one heavy dumbbell raised with both hands), cable triceps extensions (done from overhead pulley).