For an oil change, right on full, daily driving, no more than 1/2 way down the dipstick. At least on my 2003 Sable.
It all depends on what you feel your car needs though.
For example, on a car with a lot of city driving, i would let it drop down a bit more, since there will be time to top it off before it gets any lower.
On a car that goes on the interstate a lot, halfway down is a good spot, top it off there so it does not run out on the interstate, and at high speeds.
I drive a balance between the two, so 1/2 way up my dipstick (1/2 quart) is about right for me. The sable leaks 1/2 a quart through its drain plug (i have to put a new pan on, found this out after i changed the oil, the leak not the pan) since it has a threaded end and a rubber seal on it, so i have to just remember to add 1/2 a quart before it seals properly. Next change that is being fixed.