at the Top of the list it must be "Rugby Union" since Rugby World Cup is the 3rd biggest sporting event after Olympics & FIFA WC (Super bowl is only 1 game that's why it's not higher on the list)

it's similar to American Football and very popular in commonwealth counties such as England, Australia, NZ, South Africa, Scotland, even Canada also popular in France, Ireland, Italy, Argentina, Georgia, Japan........ect

http://www.youtube.com/watch?v=9sSc5ZPK7...

Tutorial: http://www.youtube.com/watch?v=IEQyCcage...

Other Sports uncommon in the USA are:

Aussie Rules Football: such an amazing sport 10 Times better than soccer, Fast, High score, And brutal

http://www.youtube.com/watch?v=Dtmu-1kMF...

Rugby League: it's simmilar to Rugby union but not the same (there's big differences)

http://www.youtube.com/watch?v=K100iSuN-FE

Hurling & GAA Football: both sports are Irish

Handball: popular in Europe, north africa and middle east. Biggest league is HBL (germany)

Cricket & Field Hockey: Very popular in India and other nations

* P.S: The Eagles (US rugby union national team) have succeeded to qualify to all Rugby World cups since 1987, and won on two occasion the Gold medal in the Olympics back in the day, and there's a lot of potential for professional league in up coming years and hosting the World Cup, Beside the 7s versions of the game is being held every year in Las Vegas

http://www.youtube.com/watch?v=WYDbARvBffk

One of my favorites to watch, haven't got to play it yet, but I watched it when i went to Ireland for a week. That would be hurling, it is very popular in ireland, it is also an ancient sport. In ireland they have clubs, but no real professional teams, its more town vs town. Its played with a stick, much like lacrosse called a hurley and a ball about the size of a baseball called a sliotar. It is very difficult to explain, but if you google it, their will definitely be more info on it

Yay! Someone else said what I was going to say. Beautiful but not that common in the USA is Rhythmic Gymnastics. It's sooo beautiful and it takes lots of grace and timing, not to mention flexibility.

Handball

Mens field hockey

Trampoline

Rhythmic gymnastics

Figure skating

Table tennis, or ping pong as its often called

www.youtube.com/watch?v=A8IVASo0umU