I'd say the Klipsch Promedia 2.1 (<$150) or the M-Audios. The Promedias are good value - a sub with plenty of kick and decent sound quality for a low-cost 2.1 system. For a more civilised sound the M-Audios will do great. I've also just got a pair of (<$150) Creative Gigaworks T40 for a corner which are not bad - they're not room-filling but desk-filling, and present a reasonably balanced, civilised sound.