I was in Silicon Valley the other day (all the way from Australia) and took time out to visit the Computer History Museum.
WOW!
Fantastic place, and they have a collection of calculators too, most of which are HP.
Here are some pics of the collection:
http://www.calcwatch.com/HPcollection1.jpg
http://www.calcwatch.com/HPcollection2.jpg
Also plenty of history on other calculator devices like the abacus and slide rules etc.
Dave.