Hey man, GBPF and BDFPA are the main two as Adam said. I'd have a look over at Sugden Barbell too, good forum with lots of powerlifter/strongman competitors, also has a a competition section.
I want to compete as well, probably towards the end of 2012/start of 2013 (gives me enough time to sort out my hips and squat)
My medium term goal is the qualifiying total for the GBPF British Unequipped Championships which is 570kg at 100kg and 600kg at 110kg. I reckon you are quite close to if not at those numbers already.