Hey, a question I can answer! What is important, IMHO:
Magnification: 8x is plenty, 10x is too much to hold comfortably for long periods of time.
Size: 30 or 32mm objectives are lighter and smaller, but still provide excellent viewing. Easier to carry all the time than the 42-44mm bins, but those are brighter, so it's a tradeoff.
Most people buy roof-prism binoculars these days. Look for Fully Multicoated lenses, Phase Corrected, and BaK-4 prisms. Once you start looking at the nitty-gritty details, I always look at the Field of View, which is extremely important and yet varies dramatically between models, and the eye relief, same issue.
+1 to the comments about not looking through the high end stuff right now. Leica, Swarovski, some of the Zeiss -- off limits or you will end up going crazy. For a serious birder, binoculars are like tripods (see the bythom article on buying a tripod) -- you start low and end up progressing through ever more expensive glass until you finally break down and buy the top end. (Ask me how I know this....)
For me, the perfect birding glass is an 8x32 roof prism, phase corrected, with a ~400 foot FOV and as long an eye relief as I can get. Pentax, Minox, Swift, Nikon, EO Ranger (though the newest Ranger is the 8x42, I don't think they've upgraded the 8x32 yet;) all make good quality binoculars. In our house right now we own the Pentax SP 8x32, the Leica 8x32 (mmmmmm), and the sadly discontinued Nikon 8x32 SE porros, one of the finest birding optics ever.
You might check out the Eagle Optics Ranger series
. They have all the high-end features, but should come close to your budget. In fact, a phone conversation with the very helpful folks at EO will help tremendously. They carry everything, and are well-versed in the tech specs and features. (Disclaimer: I am just a very satisfied long term customer.) http://www.eagleoptics.com/
Good luck and happy birding.