The best car I had for mileage was a '91 Tempo L. Totally stock, with the exception of a glasspack muffler that replaced the catalytic converter. 2.3L HSC manual with 255k miles on it. Two different times, when driving 512 miles on the highway, using the same gas pumps to fill up, same driving times (different months, but same season of same year, on clear days), I was able to use 10.06 gallons, which is just shy of 51 MPG, averaging 70 MPH. I don't know how I did it, but it happened. Otherwise, the car routinely gave 46 MPG, and would cruise at 120 doing about 4600 RPM. Sadly, it couldn't handle worth a darn, and I ended up rolling it.
Currently have a '13 Focus as my daily, 5 speed manual, and it gives about 32 MPG city, and 38-40 highway, cruising 70. Bone stock.