GUIdebook - Dedicated to preserving and showcasing Graphical User Interfaces. Includes various images, icons, posters, news items and other related materials. - http://www.guidebookgallery.com/
OldOs.org - Resource for utilities, history, and much needed to get many old computers up and running, physically or in emulation. - http://www.oldos.org/
Operating Systems History - A Brief History of Computer Operating Systems from the mid 1950s on. - http://www.cs.gordon.edu/courses/cs322/lectures/history.html
History of the AmigaOS GUI - Dedicated to the preservation and restoration of the Amiga Workbench's history. - http://www.gregdonner.org/workbench/