What To Look For:
When you buy a surge protector, try to find something better than the $5 or $10 power strip things. Although they are slightly better than nothing, they are notoriously unreliable and most won't tell you when they are no longer protecting your equipment. One good surge and your protection is gone—but they continue to function as a power strip. Very tricky...
Also, when looking for a surge protector, look for one that features a phone line "pass through". Telephone wires can deliver a potent surge into your computer. I've repaired (and seen) more than a few computers that were damaged due to telephone line power surges.
In fact, phone line surges are more likely to cause damage than power line surges. Why? Your computer's power supply acts as a built in surge protector (not a great one, mind you). Even if a surge sneaks through your regular surge protector, the power supply may prevent it from doing any damage.
That said, just because your power supply does some remedial surge protection, it's no substitute for the real thing. Computers get damaged on a daily basis due to lack of surge protection. But I digress...
Back to surge protectors.
A good quality surge suppressor will cost anywhere from $20.00 to $100.00 and be "UL" listed. It should also feature an indicator light that tells you when the surge protection circuit is no longer functioning.
Now, when you start talking surge protection, you sometimes run across folks babbling about clamping voltages, response nanoseconds, and joule levels. Although that is a valid way to compare various surge protectors (and make the speaker look knowledgeable), not every protector gives you that info—and who's to say it's even accurate? Let's look at the "down and dirty" method of finding a good surge protector.
The easiest way to tell if you're getting a quality surge protector is to look at the "connected equipment" warranty. I like the ones that cover connected equipment for up to $15,000 or more. I figure it they are willing to risk 15K +, they're probably selling a good piece of equipment. If it doesn't have a connected equipment warranty, set it back on the shelf and keep a-walkin'
Sure, it's not as geeky as going into a computer store reciting clamping voltage figures, but for most people it will be every bit as effective.