I've been training for 14 years or so, and at their biggest the pumped just over 18".
I don't really do much for them directly, I can easily do 15 reps with 135 for bb curls, or french press about the same, but the big compound lifts work them well enough for me at the moment:
Bis: Deads, chins, Rows, Cleans
Tris: Push presses & Jerks, Benches, pullovers, dips
In fact the only exercise that I do that does not work the upper arms is of course SQUATS!