I realize that I'm probably the last person to hear about them, but I've just recently discovered Flogging Molly. I'd been listening to one of their songs for ages, without really knowing it, as it's featured on Tony Hawk Pro Skater 4 (Drunken Lullabies).
I have a fairly eclectic taste in music and these guys fit right in. They've got a celtic sound I love and their songs are all really well done. Over all the music is pretty upbeat.
Anyway, if you like that Celtic-y, Ska-y, Punk-y kinda sound I would suggest you check them out if you haven't already.