I am failing to find good initial links but I know I have seen more than one retirement/memorial quilt. I think the plaids and stripes lend themselves well to simple star shapes, you can play with the woven design and angles like in a Lemoyne star, or just a more simple Ohio type star. If you also have the blue chambray solids, you can make an alternating 9-patch which will make a single Irish chain around the stars.
Basic Rail Fence strips can look really good with men's shirts.
Just as a general thing, when I harvest fabric from shirts, I mostly just deal with the large solid piece from the back, but there are some other good pieces of fabric, I just cut it apart at the seams.
On the other side of things, I have seen pockets from shirts used. Either all pockets cut into consistent squares, or some pockets mixed in as a place to put some sort of note or trinket of remembrance.