The "giant magnetoresistance" (GMR) effect was discovered in the late 1980s by two scientists working independently: Peter Gruenberg (Julich) and Albert Fert (University of Paris-Sud). GMR has opened the way to the new field of spintronics and to a revolution in the field of information technology.

A summary of the GMR effect and in particular the contribution of Albert Fert and Peter Grunberg to this field can be found here.

The reviews by Prinz and Wolf et al. provide a broader introduction to the field of spintronics with some discussion on GMR.

Other helpful reviews that focus more closely one GMR are the ones by Camley and Stamps, Parkin, and Chien.

Also the IBM GMR website provides a very simple first introduction.