http://www.blogmusik.net/ The first one is 'an online iPod'... basically search and listen to just a full version of most songs. Fairly good selection.
www.pandora.com - enter in a band or song, and it'll start listing other songs that you may like... you can rate them and such... it does a pretty good job of matching up songs right, at least after you've rated a few songs. You can only skip a few songs/hour per search, but still... Both sites i'd recommend checking out. Pretty damn large library on this one too.
(or it had songs from the rarest artists i've ever heard of)