Steermouse
I forgot to mention one other application that is an early install: Steermouse. Do you have a multibutton mouse, but don’t want to install drivers that make Leopard cry? I tried USB Overdrive as well, but Steermouse was the first to support my Razer mice, so that is where my US$20 went.
Prodded into memory by a post over on Daring Fireball.