RBF is pretty awesome at ska. what I really like about them is the fact they've been around for awhile and still are staying ska, unlike most other ska bands that started off completely ska and are now completely punk. *cough less than jake cough*

My fav RBF album is "Why Do They Rock so Hard?" -although most of their albums have good stuff on them.

If you like these guys, you'd love the Mighty Mighty Bosstones, (early) Less Than Jake, and the Aquabats. some other people you might like is the Toasters, Mustard Plug, the RX bandits, Five Iron Frenzy, Catch 22, Streetlight Manifesto.
...I could go on. (I like ska.)