I selected two: Tennis and Horse racing.
I'm a avid fan of Tennis, although I was not active in the other forum, but I used to post a lot of that thread. But there are a lot of tennis fans there so I will leave it up to them.
As for horse racing, it's local only though, I'm not into the US or Middle East horse racing.
I also bet on boxing, but it's not on the list. Football is not famous on our country, unfortunately, I do watch them from time to time and also NBA. Bet a couple on games that interest me.