We used to go to Friendly's Ice Cream and Sandwich shops quite often when we lived in "their territory". They made a good cheeseburger and the sundaes and shakes were good too. I believe they have dropped in quality over the years, but we haven't been in one for several years. http://www.friendlys.com/
Braum's in the OK-TX area is a cleaner version of the same thing. Kind of a semi-FF sort of Burger place with very good Ice Cream.
Check their menu- http://www.braums.com/
Culver's Is definitely more of a FF and custard place. We like their menu a lot. http://www.culvers.com/menu/default.aspx