After you figure out what you're going to use them for (ie. graphics work and text would be different from video and gaming), you can determine what kind of minimum specs you're going to need.
In general though, I'd suggest at least 200-235nits brightness and at least 250:1 to 300:1 contrast, as minimum specs. If you're going to be doing things with movement (video and or gaming), look for a low total response time (25-40ms). I'd personally suggest looking for something with DVI and VGA inputs, though if you are using good video cards with clean 2d, you can get away with just VGA.