If your PC is pulling double duty as a media center, I can't speak highly enough of the Logitech Z Cinema speaker system. It's a 2.1-channel surround-sound powerhouse that cranks out 180 watts and comes with a sweet media-center remote.
Originally priced at $300, the Logitech Z Cinema is on sale for just $79.99 from TigerDirect. Shipping runs a hefty $22, but that's understandable; these are hefty speakers!
The system consists of a subwoofer that plugs into a USB port and two desk-friendly satellite speakers. On one of the satellites you'll find both headphone and aux-in jacks, the latter for connecting, say, an MP3 player.
I should note that these are new speakers, not refurbs, and they're covered by a two-year warranty from Logitech. (TigerDirect's product page says 12 months, but it very clearly says two years on Logitech's site.)
CNET hasn't reviewed the Z Cinema, but PC Magazine gave it high marks. Surprisingly, the magazine dinged the remote for being complicated, but I find it very comfortable and intuitive. The volume-control wheel in particular is just awesome.
In short, I adore these speakers. They're perfect for a den or bedroom where the PC serves up music, movies, and the like. And I'm wild about the price; you really are getting a $300 speaker system for just over $100 out the door.