I know very little about music, and even less about what constitutes 'alternative' music, but here's a few of my lesser-known favourites:
Vanilla Ninja: This group is from Estonia, and apparently they were really REALLY big there, but nobody I have mentioned them to here in Canada knows them. They haven't made anything for a few years, but they are my favourite music group ever. And two of the girls are REALLY hot
:D:D
Anyway, going through my playlist for groups that aren't that well-known. (as far as I know)
Jakalope: This group has some good songs too. Again, I'm terrible at classifying music, but whatever.
Maren Ord: She was pretty big locally for awhile. I went to high school with her, and she released a couple CDs, but she's married and raising a family now, and hasn't released any music for a long time. (that I know of; haven't talked to her for a couple years either, as she moved away)
Porcelain and the Tramps: This group has some bad language, so if you are against that, stay away. I like their music anyway, even in spite of that.
Ayria: Her songs are longer than most people's (warning to peopel with ADD! :p) I think she'd be classified under 'trance' music, but I'm not sure.
Sirenia: This group is what would be called 'pagan' music, I'd think, since that's the theme of a lot of their songs. "The Other Side" is my favourite song from them.