Here's my rankings by what I think their popularity in the U.S.A. is (among TV viewers and such).
#1. NFL football. Granddaddy of all sports. For 17 weeks of the regular season (encompassing 16 games per each NFL team), plus 4 pre-season/exhibition games, plus the playoffs and culminating in the Superbowl, followed up for those that just can't get enough with the Pro Bowl, it's the big kahuna.
#2. NASCAR. From Daytona to Taladega, to Darlington, Loudon and beyond. NASCAR rules for approximately 40 weekends, most especially on the super speedways. It's overlooked by many, and could be just a bit below my next choice, but I don't think so. I give NASCAR the edge here.
#3. NCAA College Basketball. March Madness is all you really have to say. Once the Road to the Final Four starts up many people get the fever and it doesn't end until the Final Four is done or their pool picks have all been eliminated.
#4. NCAA Football. Some people would put this at #2 but I think this depends a lot on where you live, who your favorite local team is, or which school you attended. I think it's less popular than the NCAA Basketball sport is, but maybe you disagree.
#5. MLB Baseball. This may not be as high on many other lists, so perhaps I'm way off with putting it here above some other sports, but I think America's pasttime still rates this highly.
#6. NBA Basketball. Until the playoff season arrives this sport doesn't even really show up on my radar. I know it's played, and I occassionally watch games, but I don't go out of my way to see them on TV, and especially don't go out of my way to see them in person.
#7. PGA Golf. Not quite up there with the top half of my list, but still quite popular for many people.
#8. Tennis. A notch below golf. Suffering a good bit because of a lack of stars in the men's game. The sport needs a few heroes and villians both, and currently seems to be lacking a bit.
#9. NHL Hockey. Some might put soccer above this one, but again I don't think so. While the lockout hurt the league and it's teams, the NHL has a dedicated core of followers and an appeal to blue collar people.
#10. Pro Soccer. Some consider it more popular than I would, but I think most of the U.S.A. doesn't know it even really exists.
#11 and below - everything else. That would include Track and Field, Indy Racing, Boxing, and more.
Is my list wrong? Out of order in your opinion? Speak up and put me right...