Just bought a used APC SUA1500 off ebay, and in the first 3 days of having it, it kicked in in the afternoon cause the line voltages dropped below the set value. Always knew the lines going into my house were crappy, just didn't realize they were THAT bad. Of course, this is also during the summer of rediculous heat, so all the AC's here go into overdrive in the afternoons. Brown-outs have been quite frequent.
What PSU do you have in your computer? That is a good place to start when trying to find a big enough UPS.
I've had Belkin, APC, and Cyberpower UPSs and I dont really have any complaints about any of them. The APC was the only one with a user replaceable battery but by the time those batteries die it is usually better to just buy a whole new UPS, lol.
If you have the bucks go for an APC. If not Belkin and Cyberpower are good alternatives.
Crashman had a good link for replacement batteries for APC. They aren't that expensive compared to buying a new UPS.
I buy used UPSs for cheap. I believe UPSs have better protection for my computers,TVs and stereos, if the batteries are bad for my stereos and TVs, no problem, not like I need to save data on a stereo and TV.
Beware of cheap power strips.
Like Folken said, you can't go wrong with APC, Belkin and Cyperpower. You might be able to find an inexpensive UPS at a thrift store or ebay, the batteries might be bad but you can get replacements cheaper then buying an UPS new.
I don't have any Belkin or Cyberpower UPSs but from what I heard they are good. I use APC. Being able to replace the batteries is very important!