Simboarding @ Virtual Sports Nexus is by far the most fun I have in SL. It is located on the Blue Horizon sim and is a cross between skateboarding and snowboarding. They have a freestyle park course, halfpipe, and soon a racing course. They have competitive events 3 times a week. The pro comps on Sunday are brodcast on Treet.tv. It is by far the best sport in SecondLife IMO. I also enjoy base jumping and skydiving at Booville. They have a great setup and I can spend hours there.