I've done a lot of research on fuel economy cars. The first place you might want to look at is (
www.fueleconomy.gov). I have 3 hybrid car brochures from Honda. Honda Accord, Civic, Insight. Accord gets crappy miles, Civic is alright, Insight is super.
Remember, you don't want to buy a, expensive car because then it'll take more years to actually notice the difference in the money you save.