I wear a size 15 and have flat feet - to start.  I blew out my ankle in high school and have NO ARCH in one foot.  My ailments aside, these socks fit GREAT and seem to actually provide some support which, if you've got big feet, you need all the support you can get.

These aren't cheap, but I would consider them a value for going to the gym, golfing, anything where you don't want to look like a clown cause your socks are so damn big.