Folks often ask me for bike buying advice, mostly for commuting, so I thought I'd drop in a few links here to bikes that look good to me for commuting on. Not that I've tried them all, but if you try them and like them, and they're in your price range, I think you'd be just fine buying them :)
You definitely have to test ride a few bikes to see what you like. Try a bike with flat handlebars and a bike with road handlebars.
Commuter bikes sorted by price:
Other quick tips: