Depending on your weight, age, experience and fitness level, there is also the recumbant bicycle to consider. You really need to know what riding you plan to do. That is probably the hardest part. You might even consider buying something really inexpensive from ebay or the classified ads in you paper just to see what kind of riding you like to do and where. This is useful if you are just starting out from scratch. Then if you love that bike but wish for better, or hate that bike and wish for different, you'll have a bit of knowledge before plunking down big bucks. The LBS might even have a left over used bike for $50-100 just to get you started.
I'm a roadie, but that, and all of the above is merely opinion.