Enterprise and other discounters will rent you a Toyota Yaris, which not only looks sweet, but gets an impressive 35 mpg on the freeway. You won't have much room for your luggage, but you'll save up to 50% on fuel over a full-sized car. Economy-sized cars are also much cheaper to rent than hybrids. Hertz, for example, recently offered a Toyota Prius (which gets 45 mpg on the freeway) for $48.99 per day versus $28.99 per day for a petite Hyundai Accent (33 mpg).