I think the best way to find new music is through word of mouth. Talking to people in the industry made me discover some pretty awesome bands/groups/artists. Also, things like Pandora, Last.Fm, and Pure Volume are great for discovering artists that are similar to what you already like.

I personally love Florence + the Machine at the moment. Her vocals are just amazing. Not much guitar there though but amazing none the less.

I also love my boys in Taproot. They're a bit heavier for the most part. I would suggest looking up anything from their album "Blue-Sky Research".

One of my favorite bands of all times has to be Brand New.

Those will be easy to find online at least.

You may also like "The fabulous Miss Wendy". I don't personally like her vocals but she has that old style guitar going on. I'm pretty sure she has a Youtube. She toured with a friend of mine a while back.