You need to be a little more specific. What do you want it to do, how many speakers do you want to run.
Basic setup:
AV Receiver
2 Front Channel Speakers (Left and Right)
2 Surround Backs (Left and Right)
1 Center Channel Sepaker
1 Subwoofer (or 2)
This is a 5.1 or 5.2 surround system
Or another option:
2 Front Channel Speakers (Left and Right)
2 Surround Speakers (Left and Right)
2 Surround Backs (Left and Right)
1 Center Channel Sepaker
1 Subwoofer (or 2)
This makes up your 7.1 or 7.2 surround system. You will need digital AV cables (ex HDMI) from your Source (ex. Blu-Ray player) to your receiver (or HDMI directly to your TV and optical audio to the receiver, if your receiver is not an Audio/Video receiver or not capable of video pass-through) and if you do use your receiver then another Digital cable from your receiver to your TV. The AV Receiver must be capable of full digital surround modes (Dolby D, DTS, DTS-HD, Dolby-HD etc....)
That is your basic home theater setup.
Or you can buy a Home theater in a box, but if your looking for a great system for hours of use, I would not go that route. Those are usually for people on a budget, or who just simply don't feel the need to build a higher end system.
I can help you further, just need to know exactly what your looking to do, and how much you are looking to spend.