lately, i've been really digging Pandora.com

you type in the name of a group & it programs a radio station of music in that
vein... for example, I typed in Zombies and I've been grooving to The 
Action, Castaways, Dave Clark Five, Who, Nazz, The Roosters and all 
kinds of harmony pop for the last 30 mins.... you guide it along if 
you
don't like a track...

they don't have everything in their database but it's great for 
creating a music vibe and be surprised by
the cool choices it makes ("At The Place" by Dave Clark Five!!!!!)

last night, i needed music to work to so I typed in Bill Evans and 
got cool piano jazz for hours...

wow, it just cued up "Triad" by The Byrds...