I've been using the USDA database more lately, it tends to do a better job with quantities and nutrients. None of this 'a serving of flour is 1/4 cup' nonsense that's required on nutrition labels.
See USDA foods database
USDA uses 125 grams/cup for unbleached AP flour (4.41 ounces.)
I still tend to use KAF's flour weights (4.25 ounces/cup) as a starting point, though many recipes seem to be based on a higher weight/cup basis. But it's easier to add flour than take it back out again. (And an enlightened author/site should give important quantities in both dry measure amounts and weights anyway.)