i definitely prefer repetitive or ambient, non-lyrical music. sometimes i'll even put on sleep-music albums
a couple albums in particular standout: * philip glass & ravi shankar - passages * kawabata makoto (of acid mother temple) - infinite love - i think this album is tuned to my brain's beta wave frequency. its like sonic ritalin * robert rich - somnium
for more energy i usually look to montreal. godspeed and silver mt zion always please. a little bit lesser known is "do make say think" who are one of my desert-island bands.
and sometimes, just sometimes, i just have to listen to dancey trance music. check out onnomon (who is also, by the way, my brother and an old timey hacker)
as a side note, i mostly use rhapsody for online music. its just straightforward and easy... well worth the monthly subscription fee. if only the site was a bit faster.
as far as free services go, i really like the spirit of last.fm but pandora's recommendations are consistently better.