Here are a few I found on a quick search:

University of Nebraska
University of Kentucky (Gaines Center for Humanities)
College of William & Mary
Maryville College
Monmouth College
Lyon College (Arkansas)
Lees-McRae College
Alma College
Virginia Military Institute
Warren Wilson College
Oregon State University
Michigan State University
University of California Riverside
University of Tennessee
University of NC Greensboro
Furman University
Auburn University
Clemson University
Notre Dame (Marching Guard)
Western Carolina University
University of Wisconsin (Wisconsin in Scotland)
University of Chicago

I was limiting my search to American institutions -- there are many colleges and universities in Scotland, England, and Canada that have their own tartans.

And I recently received commission to design a tartan for VA Tech.

Aye,
Matt