I remember either Shutsumon or AM Harte had a flattr button on their site. I heard it has better uptake in the EU than here...
Cheapass fiction lists a few who use it as well : http://cheapassfiction.com/2011/11/20/flattr-club/
I've often wondered how well that works for people. I should try it sometime.
Flattr has actually been around for a long time. When it first started I stayed away from it because in order to receive donations you actually had to donate yourself, and I didn't see any reasonable way to make it work from me. They've since changed that requirement, but I've yet to get around to trying it out.