The older Gateway self-powered ones work good if you:
1) Set them at medium volume
2) Set Win Media player with a slight smiley face EQ boost lows a few db's and highs a few db's
3) Engage the SRS enhancement in Win Media player
It's what I use at home if I'm not running the PC into the nearby QSC2402 and ACME B2's.
Here's a set. The ones here have a port on the back for "bass" that works well with the settings given IMO.
Many on eBay. A couple of years back, I bought a boxed lot of 4 sets for cheap for co-workers here on our checkout crew to use in their cubes as the sound of music through a phone speaker or garbage PC speakers drives me nuts.
If you want better, OLDER Altec Lansing's that have a sub and 2 satellites work VERY nicely. I practice through a set in my cube. Just set them up so the multi-pin connector cannot be broken by the vacuum cleaner operator on the custodial crew....been there, got the T-shirt and now keep the connector side back UNDER the desk facing a wall(impossible to get to with a broom or vacuum cleaner). Older Altec's pictured below.
All of the above have AUDIO INPUT using 1/8" stereo male plug, same as mp3 player or I-pod.