I just listened to 3 bands on last.fm for the first time (making potentially poor errors of judgement, based on a few listens)
These were all bands recommended by last.fm.
God Is An Astronaut - 8/10
Really liked this lot, lovely subtle post-rock sound, nothing too clattered or messy, some nice sounds, quite epic. I would buy "All is Violent All is Bright", definitely.
Ahleuchatistas - 6.5/10
Technically proficient math-rock with a funky edge to it, the basslines sound pretty cool, although they seem to be missing a little something. They're not too disimilar to a cross between "By The End of Tonight" and "Don Caballero", but without the moments of brilliance.
These Arms Are Snakes - 5/10
Completely unfussed with it. Messy, punkish, post-hardcore type thing (I'm sure the genre fiends will correct me on that one). I was expecting something a little more interesting at least, I've heard a lot of good things about these guys.
Those are my snap judgements anyway, when there's so much music out there to explore it's hard to give every artist much of your time. A few songs is sometimes all you can afford, which is a shame. Please feel free do disagree and call me an idiot below.