If you don't need deep bass, I use M-Audio StudioPro 3 Desktop Audio Monitors. Definitely less than $100 (I got a $25 rebate when I bought mine, which made them very inexpensive). They're nice enough looking, have an auxilliary input (for an mp3 player, say), and sound vastly better than typical "multimedia" speakers. There may well be better options in the price range, but they're worth checking out.