I voted for:
Football - The fact that the NFL season is only 16 games creates an atmosphere where every game matters so much and every big play and injury is magnified. The actual playing of football I don't think is terribly exciting, but the short season makes it very exciting and suspenseful. That is a huge built in advantage over any other sport. I can watch football in the regular season or playoffs.
Baseball - a lot of this is because I grew up playing baseball. I think it's still America's pastime. Going to a baseball game during the summer is great. Probably my #1 sport. And there are some amazing plays, especially from the infielders. I can watch this anytime during the season.
Basketball - Basketball is up there on my favorite sports to watch. Playing can also be very fun. It is usually pretty fast paced and exciting to watch. Especially in the playoffs like right now, which is when I usually watch basketball. And going to college, the NCAA tournament is one of the best sporting events in the world.
Tennis - I was never that fond of tennis until I started to play it myself. I developed an appreciation for the skill involved. And also the strength and endurance those athletes have to have to play tennis matches that can go in the 4-5 hour range. Ridiculous! I'm not very good and tennis but it's very fun to play.
Volleyball - I mainly voted for this because it's fun to play. Especially beach volleyball where you can dive to get digs. Watching volleyball is okay.
Extreme sports - I don't watch this as often as I used to but I still can enjoy it. And I respect these guys so much for absolutely killing their body. Probably some of the toughest sports. And the skill involved, especially in some of the sports, is crazy. There was a couple year period where I got into "aggressive" skating (I was never very good) and it's just amazing what some guys can do.
I didn't vote for them but some close ones:
Nascar - I never really watched much racing until a friend of mine got me to watch the Daytona 500. Ever since then I try to catch parts of the races when I can. Watching cars drive in circles can be surprisingly entertaining.
Hockey - I've watched some of the playoffs this year and it can be very exciting. I feel like NHL has a better product than they are given credit for. They just need to market themselves better. If more people would give them a chance I think they'd be pleasantly surprised. I think they are a long way from competing with the "Big 3" though.
Soccer - US soccer stinks, but if you can get some international competition it can be pretty fun to watch. I got into the past World Cup and also the past European Championships.
Golf - Can be the most frustrating game imaginable but can also be very fun and relaxing. Watching it is hit or miss. There can be great drama on the final round if there is a good race going on, but it can also be very boring if someone is just blowing the field away. Mainly I watch the 4 Majors.
As you can see, I'm at least a partial fan of a lot of sports and I try to follow along with a wide variety of things. Each sport has its own piece to offer.