As much as I like Manowar, Blind Guardian, and Rhapsody, most of their stuff isn't really all that appropriate if you are trying for the "mideval" feel. Of the three, Rhapsody is probably your best bet... They have a lot of semi orchestral/operatic music that would work OK.
If you want to go for the "bardic" feel, try Heather Alexander, Leslie Fish... go to
www.firebirdarts.com and check their music index for some good bardic folk type stuff (A lot of it was made for fantasy worlds anyhow), or
www.heatherlands.com to check out Heather Alexander. Both have samples you can listen to. Check out on Heather's site a peice called "March of Cambreadth".
I also like Elven Drums (
www.elvendrums.com), but they are most definetly not for everyone. Their site has samples, though, so check it out if you like.
For just general background stuff, most of the major ones have been mentioned... Though, for the record, the soundtrack for the DnD movie isn't bad, if you can get it. I'll also second Conan, and if you can find them, the Final Fantasy soundtracks are pretty good... So is the Ultima one... It's great, in fact... (There might have been two), but they are pretty hard to come by.