If you don't want to spend too much money on a second car..

2011 Hyundai Elantra is good. Compact car of the year by CR. 40mpg highway.

If you want a bigger car, Hyundai Sonata or 2011 Kia Optima are both good, and they are among the safest cars in their class, the same class includes MB C300, which is also very safe.

If you don't want to keep the car too long or not sure, then buy an used one. But the used cars are usually not that fuel efficent as new 2011 models.