Buy a diesel. Diesel cars can often get better mileage than comparable hybrids. Getting a diesel car also allows for use of bio-diesel or even waste vegetable oil (WVO/SVO) fuel.
Buy a hybrid. Not only do hybrids give you immediate savings at the pump, the U.S. government and your local state offer tax breaks for people who use gas-saving cars. Federal deductions for using gas-saving cars can be as high as $2,000, but check before buying to see if they're still in effect.
Buy a smaller car. Generally speaking, smaller cars are lighter and get better mileage.
Buy a motorcycle or scooter instead of a car. They are cheaper and often get 70 MPG or better. Riding gear is available for most weather conditions. A good example is the Kawasaki EX250, which costs about $3,000, gets 60-70 MPG at highway speeds, and can go 0-60 MPH in under 6 seconds!