how much do you want to spend? PC speakers are probably not the best option, theyre designes for best perfomance close up - you'd probably be far better going to richer sounds, buying a cheap hifi amp and speakers.
failing that, I have a Creative sub/satellite 2.1 system here that for the price and size sounds phenomenally good. Argos do their top of the line stereo set for about Â£70 I believe. but another Â£30 would get you a Cambrdige Audio stereo amp and some JBLs from richers.
You can get an entire 5.1 system from Asda, including Sub Woofer with built in amp for Â£49.99.
Unless you lounge is huge they will do. Mine is 33 ft x 18 ft and turning them up full whack just deafens everyone in there , sound quality is way more than I expected for Â£50 as well. I believe they do a 7.1 system now for about Â£20 more.