Depends how much you want to spend. The best simple option is to get a logitech Z906. It's about $330
If you want better than that, consider getting a receiver with 5.1 or 7.1 direct inputs (a cluster of 6 or 8 RCA inputs on the back labeled front/sub/side/surround/back). I have a Harman Kardon avr 1600 and would recommend that (also the 2600 or 3600, but the newer 1650/2650/3650 line lack the direct inputs.)
Yamaha also makes a lot of receivers with direct inputs.
Then get a nice set of small speakers. I'd recommend any of the following:
Energy Take Classic 5.1
Energy RC Micro 5.1 (I have these)
Martin Logon MLT-2 5.1 (or MLT-1)
Klipsch HD 500 5.1
JBL Cinema 500 5.1
They are all up for sale on Newegg. The trick is that audio components fluctuate in price wildly. Watch prices for at least a week, sometimes you can get a really good deal.
Newegg has the best sales but always check there prices against a web search. If you get lucky you can get a really good system for about $550. Otherwise it would be closer to $800. (Also buy all your cables on Monoprice.)
unless you provide more information such as budget, type of setup wanted, etcetera i refuse to answer. there is another post just like this (look for it) and the poster abbandoned it. there are quite a few good ideas listed in it.