I would also vote for the mountain bike. There are many makes of "sport" versions out there. If you are looking for a lower end bike, I would go to your local bike shop and look at $300 range bikes. This weekend I went to help my GF pick out a new bike. She needed one primarily for biking downtown to class. We got her a $220 Raliegh mountain bike. It has the adjustable riser handlebar stem, which is nice for the casual rider. This bike also had semi-slicks for the mostly city riding it will see.

Look around at the bike shop and ask a lot of questions.