I second The Aquabats. The only Catch 22 I really like is with their original singer, the new guy gets on my nerves.
See: Streetlight Manifesto.
I <3 ska. The Arrogant Sons of Bitches is by far the best ska band in existance, although they're technically broken up.
http://www.asobrock.comska totally worth checking out (not already mentioned in this thread):
Bandits of the Acoustic Revolution- An all acoustic project headed by the same guy who founded Catch 22 and Streetlight Manifesto. Far from typical ska.
Bomb the Music Industry- Essentially the same band as ASOB, but with a new horn section and keyboardist. They're awesome.
Dalys Gone Wrong - A NY ska band without a horn section. They're amazing! Really fast vocals with an intense punk-rock flair and combine elements of other genres in the same way Leftover Crack/Choking Victim does.
Edna's Goldfish- Who cares if they broke up 5 years ago? They still rock hypothetical socks into a clear "off" position.
Forces of Evil - Bouncy horn lines and a return to the bubblegum ska of the late 90's. Headed by Reel Big Fish's Aaron Barrett and backed by the horn section of the late Jeffries Fan Club.
High School Football Heroes - An amazing band from Long Island, NY. Really. It's hard to describe their sound, but it's generally "fucking awesome" and is the only thing that can please all of my friends (a group with rather diverse music tastes)
Long Shot Hero - Totally rocktagious band from PA. Their lyrics are pretty emo but their melodies are ridiculously intoxicating. By far some of the best music I've ever heard.
Premarital Sax - And old local band with some amazing tracks. They broke up a while ago, with members moving on to form High School Football Heroes and Three Day Weekend.
Razbari Sumthing - A suprizingly delightful ska band from Syracuse, NY. They aren't too serious and thus write songs about unicorns and the like, with the occasional inspirational ballad about comparing life to a wet floor.
RX Bandits - If you've never heard them/of them you're very deprived. Especially since they're pretty well known. Their sound has gotten a lot more matured since they started playing music, growing from a stereotypical ska band to a vauge indie-ska band with some intense horn lines.
Stray Bullets - Amazing punk-ska band out of Boston. No horn section and very gritty, but with brilliant melodies and nice guitar work.
Subb - For a long standing Candian ska band with several LP releases they're not very well known, but among my favorites. They're simply awesome.
Suburban Legends - Um, these guys are lunatics. Catchy/bouncy horn lines coupled with some rather odd stage acrobatics.
Too Short Notice - A pretty well known north east ska band. Fronted by a female vocalist they have a rather unique sound and tend to please.
There are a ton more but I don't feel like looking up their websites and writing short blurbs about them...