There are:
Power Strips.... just serve as an extension cord with additional outlets. Price $5 to $25
Surge Protectors... actually serve to prevent large electrical spikes from reaching expensive equipment. Most Surge Protectors are $10 to $60 and many will also serve as a Power Strip with addition outlets. Easily confused with Power Strips, especially because of price similiarity. Check for warranty regarding electrical spikes. Monster Cable, Panamax, Belkin and many others will over a significant warranty (free) for equipment items that are connected to their units and damaged by electrical spikes.
Line Conditioners.... eliminate EMI and RFI noise. Also serve as a Surge Protector, and in most cases, a Power Strip. Prices starting at $30 and UP. Surprise, surprise, Line Conditioners look much like Surge Protectors and Power Strips. Same manufacturers.
Things to remember....
don't send somebody (the wife, kids, your cousin Dave, or your Mom) to buy a Power Strip, because that is exactly what you will get... a Power Strip. Sending them for a Surge Protector, will still most likely result in you getting a Power Strip. These items all look alike. Sending them to some stores for a Line Conditioner will result in you purchasing a $350 rack mounted Line Conditioner. A bit of overkill.
Connections. You can never have enough outlets. Unless specifically adviced against, if at all possible, have an entire HT routed through one surge protector. If a single surge proctector is not possible, then segments should be grouped on a surge protector. In other words, the TV, cable box, and VCR should be on one surge protector, while the Receiver, DVD etc should be on another surge protector, if all components could not be on a single surge protector.
Remember cable, telephone, and other equipment items that may be connected to the HT system should be connected through the surge protector.