(a few)
The Fantastic Frenzy, FIF, has been around since 1996 and hail from Colorado. If you want some good tunes off the FileShare prog you probably use, try "Oh, Canada," "Ugly Day," and "All of the Hype."
The OC Supertones have been around since the early nineties. Originally called "Saved" they decided to go Ska and became the Supertones. Check out "Supertones Strike Back," "OC Supertones," and "Never Wanna Fall."
Reel Big Fish. I don't know a damn thing about them, but some good tunes are "Down in Flames," "Scott's a Dork," and "We Care."
And some other good bands are Less Than Jake, The Insyderz, and the Mighty Mighty Bosstones. Boy, I sure do like Ska. On the Punk end, I'd recommend Dropkick Murphys and Me First and the Gimme Gimmes. Good stuff.