Remember that the triceps make up the majority of your arm size ....

thats true..but i want to kill the bi too..

muscle milk

Your arms, as a whole, get worked regulary throughout other body part workouts. Then i am sure, as I used to do, you hammer the hell out of them on their own special day. So in essence, you are overtraining them if they have stopped growing. I drasticly reduced my arm workout to include 2 standard lifts for bi's and two for tri's, nothing more. I go very heavy and keep reps around 8 for all 4 sets of each excersize. Then I avoid hitting again directly for 7 days. works great for me but we are all different.

I like to work them on their associated days (back iwth bi's, chest with tri's) so they get plenty of rest after...

Just hit em up with plenty of heavy exercises like straight bar curls, preacher curls, dumbell curls. Just don't overtrain.