If you want really good protection, look for something that has a battery back-up feature, EMI/RFI filtering, and automatic voltage regulation. Those units are usually more expensive, but they do more and give you more protection. Look at products by Furman that have a "PF" on the end of the model #, that stands for "power factor". That means the unit has ability to hold a charge to provide correct voltage in the event of a sag as well as limiting peaks. They also provide power in blackout situations. Good for rear project TV's and front projectors. Tripp Lite also sells excellent equipment. The HTRL15UPS is what I will be buying this week. Excellent piece and for a reasonable price. Don't buy into the different "levels" of power filtering. If it doesn't filter all of it, don't buy.
(I do work for an AV dealer and I did a LOT of research on this stuff. I have been told by manufacturers (of audio gear) to use voltage regulating systems for any sensitive electronics; and no, I'm not a dealer for Furman or Tripp Lite).
Good luck.