Ive got logitec z-340. Sweet in their day, but a little out of date right now. As for the Z-5500, they r so uber cool its impossible not to like them. They have the best sound around. Id go with those.
Sometimes http://www.woot.com has 5.1 surround sound computer speakers for $35.00 shipped. You have to catch them though, they sell out fast. Woot only sells 1 item really cheap per day.