The mod 2 cohomology of the linear groups over the ring of integers, by
Dominique Arlettaz, Mamoru Mimura, Koji Nakahata, and Nobuaki Yagita

This paper completely determines the ring structure, with an explicit 
description of the generators, of the mod 2 cohomology of the linear groups 
GL(Z), SL(Z) and St(Z) over the ring of integers Z, and its module structure
over the Steenrod algebra.