Not sure what you think of as medium sized, but I know a lot of Business-type kids who have cross-shopped Wake Forest and Richmond. Not terribly walkable although neither is Wake Forest, but it is easy to get from either to their nearby downtowns.
I would also second the suggestion of looking at Bucknell, again a popular option for kids I know in this space, but that is much more in a rural setting.
Finally, I might check out Lehigh. Big Greek scene, very good College of Business, and a walkable commercial district (as long as you don’t find hills intimidating).