I've got a APC something or another. $45 shipped from newegg.com:
http://www.newegg.com/Product/Product.asp?Item=N82E16842101124

It works fine by me (though I work on a kitchen-sink-replacement laptop all the time at home - so I only use the UPS for my external HDs - which I run my Virtual Machines on and don't want to lose in the middle of anything). The software seems a tiny bit sluggish on startup some times - otherwise it's fine, lightweight, etc. and will instruct my machine to hibernate based on a couple of simple profiles (i.e. do i want to keep my machine/stuff running as long as possible before powering down, or do i want to conserve battery and power down almost immediately - either way my stuff gets saved).

I got me one of these here Belkins: http://www.buy.com/prod/Belkin_Home_Office_375VA_UPS_With_Automatic_Shutdown_Software_200_Watts/q/loc/101/10370359.html

$34!! Can't say i've thoroughly tested it, I guess I should, but it comes with software, USB connection, and a good bit of functionality for the price.

I have several (2 currently running). I just bought a Conext for about $30 from CompUSA that works great. I live in Dunedin (Tampa Bay), FLwhere it seems at least once or twice a day the power blinks. The battery backup is nice because they keep everything up. BTW, the real question is how long does your power stay off... I wouldn't expect my UPS to last for more than an hour or so (although both are rated for 2 hours... lot of good it does you with no monitor). The longer you need to make sure the computer stays up the more money you will be paying out.

Typically the power's not out that long. But to be safe, I'm interested in the kind that can send a signal (via USB) to the computer to go into hibernation.

The smaller UPSes won't run a modern machine very long, but yeah, with a USB connection you can at least get your stuff saved. The APC line has been good to me over the years, their batteries are easily replaced when needed, and their software is predictable and straightforward. Take a look at the APC 500 VA or 650 VA models.

http://www.apcc.com/resource/include/techspec_index.cfm?base_sku=BE500R

I've currently got 2 UPS appliances. Both are APC.

I use one to backup my two servers (a PII & PIII) and a wireless access point, all tucked in our laundry closet. Both of the servers are are just a tower with a power cord and network cable. I think that UPS is rated around 500VA, and I only get about 12 minutes of up-time. However, the main server is hooked up to the UPS via USB, so it gets shutdown when there is 15% power left. Unfortunatly the other server isn't so lucky and it just gets a hard power off when the UPS is depleted, unless I get a chance to remote in and shut it down manually.

The other UPS is hooked up to my power-hungy P4 workstation. I've got dual 7200rmp HDDs, 1 external HDD, a 17" LCD, plus the broadband modem and router all running off this one. It is rated at 900VA and according to the PowerChute software I've got about 30 minutes of up-time with this configuration. I have this machine setup to shutdown when 50% battery power is remaining.

We've only had the power go out for more than a few minutes once... it was out for about 2 hrs. With the modem and (wireless) router are also running off the second UPS we still had internet access the whole time... using my g/f's laptop.

I was using a Sola Desktop UPS and an APC unit as well, i am now using a Jentec Stepping UPS. The Jentec is 2.0 KVA, but due to its stepping ability can actually be 1.8 to 2.2 depending on the load.

I was put on to Jentec by some clients who where unhappy with how much the APC units are in Australia. We ended up ordering these units in bulk and getting a good discount.

Software wise, the APC is the best, the rest suck. I now don't use any software, as i find the power is back before its needed.

On my UPS i have my ADSL router, 3 network switches, a dual Xeon server and another machine.

Remember, the low quality UPS units are usually that, and often don't work as expected.

APC customer service is terrible. I keep asking them the age of my ups using the serial number and all rhachi can say is it will last many years.

Hardware wise they are good, but don't need help

Be aware that some UPS units have the battery date encoded internally and when it reaches a certain age (3yrs in the case of the APC/Conext CNB950) the frustration begins. I put in new batteries, but the UPS still reports the original age. Shutdown manger won't work right because it thinks available minutes are "- -". So I have to run with the USB unplugged. Still trying to get this resolved, but support is terrible. No more APC or Conext for me after this unit is gone - which could be any moment.