Another thing to consider is the materials. Carbon and Aluminum tend to be rigid frames which give you lots of leverage but are less forgiving over long rides. Steel and Ti are flex better and can give you a more comforable ride, especially over long periods of time. Carbon forks also add some forgiveness to the ride.
Check out used road bikes. Road bikes tend to take less abuse than mountain bikes and you can sometimes find used road bikes that look to be in mint condition.
My only other advice is to buy a bike, any bike that fits you and just ride, ride, ride so you get an idea of what you like and don't like. If you want to add more variety to road riding, check out a cyclocross bike. Cyclocross rules!!!! D.