Viking360.com sells wonderful rapidfire controllers. They have tons of presets that you can program yourself! I just got one and it's amazing. The most expensive one is hella awesome. 1 tac switch has all the guns on the reload glitches so you can reload fast as hell without using slight of hand now. The other tac switch lets you set the rate of fire. E.g.:
Really fast rof
Jitter mode = m16 shoots like a machine gun...hella awesome
3 shot bursts
5 shot burts
And a few more.