Slackjaw, Bloc Party are fairly well-known over in the UK, they actually charted in the top 20 a few times I think. Either way, they've kind of gotten lost in the clamour over the Arctic Monkeys and their ilk.
Which brings me on to my next point. How over-rated are the Arctic Monkeys?! They're okay for a quick listen once in a while, but they're nothing special, and I'm certainly not considering running out and buying all their albums and stalking the band members.