3 links
All about the IBM 1130 Computing System
ibm1130.org
The IBM 1130 Computing System, introduced in 1965, was IBM's most "personal" system to date. This site celebrates and documents that system.
IBM 360/370/3090/390
beagle-ears.com
A condensed history of IBM mainframes and their operating systems from System/360 through System/390.
IBM Archives
-03.ibm.com
IBM's own history site, with pages on many of their significant systems (see especially the "Exhibits" and "Documents" sections).