I use an
APC UPS. It powers my desktop, monitor,
router and
ADSL modem. It stays on 24/7 and I've never faced any problems. It also came with a USB cable to connect to the computer.
Windows auto-installs the UPS without the need for any extra drivers, and lets me configure my power plan (e.g. hibernate computer if battery < 20%). The accompanying software, which I didn't install, has additional features like measuring power consumption and calculating your monthly power bill due to computer usage.
The only caveat is the battery, which usually wears out in 2-3 years (as the UPS is always plugged in). My first battery lasted about 3 years. A replacement battery by Exide cost me around Rs. 1000, but I believe cheaper ones are available in the market. Given that the UPS successfully protected my computer equipment against voltage fluctuations and brown outs, I think it's money well spent.
the battery in the zebronic UPS i use at my place also lasts 1 and half year max. Had to change battery two times in last 3 years. But the battery(luminous company) costs 700rs.
Backup is 25 mins on new battery and gradually decreases as years pass. but i agree, its money well spent considering i lost my first PC to voltage fluctuations