I agree with a minimum of 1500VA. Living here in Florida with all the lightening strikes we get every spring and summer a good UPS (IMHO) is a must. They keep you running with out missing a beat. They have served me well over the years. This is the one I'm currently using on my rig:
I even have my broadband modem hooked up separately to an older UPS I replaced. Never had to replace a battery yet (knock on wood) and three of the four I have (I have three computers) are over 5yrs old.