I love Within Temptation. First heard them a couple of years ago, but it took me ages to actually find one of their albums. I was surprised to find that not many people had heard of them.
Also, I know Ash too, Shazza. Wouldn't say that I know their songs very well, but they were played from time to time on the radio station I used to listen to. I liked what I heard, though.
Just flicking through this thread to see if there are any others I know...
Oh, Sigur Ros. My friend introduced me to them a couple of months ago. They're good.
Other ones that have been mentioned, that I know: Flogging Molly, Muse, The Enemy, Family Force 5, Feeder, Athlete, James Morrison, By The Tree, Primal Scream. (I was fairly surprised to see some of those bands here... but then, I have been surrounded with people with a very similar taste in music to me for the last two years. Now I'm at uni I'm discovering that not everyone knows the same bands I do...)
Anyone heard of Frank Turner? He was the lead singer of Million Dead, now gone solo. I was introduced to him a year or so ago by a friend, but apart from her I've never met anyone who's really heard of him. His music is acoustic, and often very bitter. More of an acquired taste, really, but I like it.