Gimme Some Money v0.85
I've been jealous of Gimme Some Candy for a long time. I've hassled them to let me in but they're not accepting new artists. It's a great idea -- a tip jar with benefits. Supporters can buy items and leave a little message that gets displayed on the artist's homepage.
So I've written and released an open source clone that's pretty easy to set up. It's called Gimme Some Money. The default items are a star, heart and cookie but they can be swapped out. You can see mine (using the default icons) over on the right sidebar.
Requirements: PHP 4+/MySQL & a Paypal account
Update: fixed an IE/Opera bug and updated it to v0.86 (thanks to jason for pointing out the bug).