If this is for a basic home/small business system then the choices are fairly straight foward: APC, Powerware, and Minuteman UPS.
APC has a nice web-based UPS selection tool:
http://www.apc.com/template/size/apc/
So does Powerware:
http://www.powerware.com/UPS/selector/
Minuteman's site is a bit spare but does work:
http://www.sizemyups.com/
Personally buying APC is the safest choice but Minuteman has a nice cost ratio. I chose a couple of low-end Minuteman UPSes for 2 business PCs. They were less expensive than comparable APC UPSes.
If you want to be very detail about your selection read up on the various types of UPSes that are available. Technically the small low-end home/small business that everyone sells aren't even UPSes they're battery backup systems. Here's a few links to overall info:
http://powerelectronics.com/ar/power...ing_right_ups/ http://www.jetcafe.org/~npc/doc/ups-faq.html http://www.extremetech.com/print_art...3D12228,00.asp