I've always had a soft spot for the Ninja 250. Quick enough to be a lot of fun, dirt cheap, and it's no big deal if you lay it down a few times - which you will. After you learn to ride on something like that, you'll have a better idea of your personal tastes in bikes, and it'll make picking something nicer that much easier. A 600 isn't too much to start on if you're cautious, but it's more money, and more to get in trouble with.
