You can also change the preference keys by running the following in Terminal:

defaults write -g InitialKeyRepeat -int 10 # normal minimum is 15 (225 ms)
defaults write -g KeyRepeat -int 1 # normal minimum is 2 (30 ms)

The changes aren't applied until you log out and back in. KeyRepeat can't be set between 2 (30 ms) and 1 (15 ms) though.

I also use KeyRemap4MacBook. I've set the repeat rates to 40 ms and the initial repeat rates to 150 ms.