Computer History Museum in Mountainview, CA is the largetst computer museum in the world. It contains very interesting exhibition of mobile computers, including handhelds.
Here is a small gallery of extraordinary items, like PalmPilot prototypes.
Lots of other remarkable photos from this museum, which are not related to handheld computers are presented in the Computer History Museum gallery.
You can take a virtual visit to CHM here: Computer History Museum, Mountain View, United States — Google Arts & Culture or CHM Revolution Tour – Mobile Computing: PalmPilot.
I met the owner of this device few days ago. The guy told me that he repaired this device by himself, and now uses it for programming microcontrollers. He writes programs in C and Pascal. The main advantages he mentioned were small size and extremely long battery life.