Look at the Nashbar flatbar road bike. Good bike for the cost ($250 -$300). It would seem to fit many of your needs. It weighs about 27 pounds. It's an 8-speed with a triple crank and comes with a good set of road tires (28's).

I agree that when riding in traffic, a flatbar is preferred. It accommodates a mirror much better and a mirror is essential. Make sure you get a mirror. Have fun.