What are your needs, wattage wise? If unsure, try the APC product selector
here.
APC makes 3 levels of UPS units. The most basic units (Level 1, Standby) don't do much, if anything, about conditioning the power coming from your outlet. If you have clean power, it may not be a concern. If you don't, you may want to insert a good line conditioner between the wall and a low level UPS. Additionally, line conditioners also offer surge protection that usually is a step above what the econo UPS units offer. The output from this type of UPS is *usually* a stepped "sine" wave (as opposed to a square wave) that looks not too horrible if the UPS isn't loaded down too much, but it can look really nasty if you're pulling anywhere close to the rated output of the unit. If you find yourself running on battery power, best to shut down ASAP.
The SMART UPS units (Level 2, Line Interactive) are probably the best buys in the APC line IF you buy them
here. SMART UPSes offer true sine wave output and (mostly) acceptable line conditioning. You can run on battery power without worrying about torturing your computer's PSU (and your monitor's, for that matter). The APC Pro units are OK too, but I think they have been discontinued.
The final level of UPS unit is a Level 3, Online unit. Too expensive for home use.