I've been really getting into the minimal-luggage scene of late. One very large space guzzler is my gym shoes. I currently use a pair of New Balance running shoes which are quite large and literally take up half of my carry-on. (Replacing that carry-on is for another future thread).

Can anyone recommend for gym shoes that still offer good impact support for running on the treadmill, but can be squashed or are somehow low profile and suitable for carry-on?