What size wheels are you looking for?
If you're interested only in fuel mileage then the smaller the wheel the better. That's quite opposite of what will look good, however.
A good compromise is a set of 17" wheels. Tires are easily found, wheels are relatively plentiful in 4x108 and many wheels can be found that are lighter than the stock Ford wheels.
Feb 2011 Ride of the Month ~ 2011 Hatch Nation Hatch of the Year ~ 2011 Focus Fanatics Ride of the Year!
Hatch Nation #2