Twitter oAuth Button Set
Twibs has created a license-free, button set for Twitter API developers to use for oAuth. (more coming soon)
Button Resources

Button Set Beveled - 18,397 bytes (.gif,.PSD)
Button Set Soft - 17,577 bytes (.gif,.PSD)
Button Set Glass - 23,368 bytes (.gif,.PSD)
Button Set Light Glass - 18,860 bytes (.gif,.PSD)
Button Set Rubber - 22,589 bytes (.gif,.PSD)