I need to buy a bicycle... can anyone give me some advice?

Gas prices are way too high, plus I'd like to lighten my ecological footprint by driving less.. so I want to buy a good bicycle to ride to and from work. I found a route using google maps that is all backroads (no highway) that is 29.4 miles (1 hour by car). First, any advice on what kind of bicycle I should get, and where to look? Also, how long do you think it will take me to get to work? Thanks for the help!