Whatever you go for, get a couple of high quality U locks and a cable just to make sure the tires are secured well. Plus, many locks even just in appearance are great deterants from theft; a theif is going to go for the easiest to steal bike. Also, park it next to a more expensive bike if you can. In a theif filled world, it's always good to have bait. (Or as blasphemous as it sounds, decorate you bike with some mud and let it dry so it looks to be an old clunker.)

Also, ask your LBS if they have any used bikes in stock, or some models from last year on sale, so you can afford a good bike and wouldnt be out much if it was stolen.