Swans M10s are a good 2.0 choice, Klipsch promedia ultras good for 2.1. Neither is currently in production and you'd most likely have to find them used. Swans might have a 2.1 set out, but if so I'm not well versed in their quality.
My personal opinion based on my experience is that 5.1 isn't a good choice for computer speakers for a few reasons; 1) You'd have to go past your stated budget to get a decent set, 2) Like the 2.x choices I listed above, the good 5.1s are no longer in production, 3) I don't think 5.1 benefits games as much as films, and most computers aren't set up to be dedicated theaters nor are they in a room with acoustics suited for film watching and 4) If you -were- using a PC as a decidated home theater, you'd probably have a receiver and HT speakers.
If you're curious, I have Creative's Gigaworks (5.1) circa 2004, which at the time were rebadged Cambridge speakers. I think the sats are fairly nice while the sub is boomy. From what I've read, current Gigaworks are pretty bad, although their 2.0 set is ok if you don't mind bad bass.