Giant makes an FCR series bike that's looks like a road version of a hardtail mountain bike. Trek makes one called the FX, a fitness bike. These bikes have a more upright geometry like a bmx/mtb. but have faster gearing and thinner, larger wheels than a mtb. You can put slicks on for the street and treads on for trails. Add a rack, some fenders and you've got a commuter.
Marin makes a wide range of Street-urban-city bikes like the Larkspur. http://www.marinbikes.com/bicycles_2..._larkspur.html
Jamis makes several models, too. The Coda has gotten several good reviews on the forum and is $440
I'd stick with a quality brand rather than something from Wal-mart or Dick's Sporting Goods. Plus, a good bike shop is a valuable resource.
The 7.3 FX is at your limit, the 7.2FX is $420.
Hybrids have a bit more upright geometry; wider tires, gearing may be a bit lower, and a front suspension fork. The fork isn't needed unless you are hitting a lot of bumpy trails and on the road is just extra weight.
Comfort bikes look like hybrids but are lower to the ground so you can put your feet on the ground while still seated. Hybrids and comfort bikes are slower than the above fitness bikes.
Cruisers look cool, have big, wide tires, usually singlespeed but can also have 3 or sometimes 7 gears. Heavy, not fast. Built for style, comfort and leisurely rides at a conversational pace.
Cyclocross bikes are road bikes with drop handlebars that can take wider tires with knobby treads. Mountain biking on a road bike, though not on extreme trails. People ride them around town because the wider tires are more comfortable when hopping curbs, hitting potholes. Can also take fenders and double as a commuter.
Next up the ladder are bikes like the Specialized Roubaix and the Trek Pilot. Fast road bikes with a geometry that's a bit more upright. The gears, tires, etc. are all road bike though some models have flat handlebars instead of drops.