I liked the Handspring Visor PDAs, and I especially like the idea of the springboard expansion slot. I know it was entirely proprietory and useless with everything else, but then again it was, at least for it’s day, very innovative indeed.
One of my favourite spring board modules was the beatplus. The sounds from it weren’t nearly as polished as those that came from the Swivel Systems SG20, but for that reason I liked the edge it had on the sounds it made.
I sold mine a long time ago, and I kind of wish that I hadn’t so I could have a museum of sorts of these old devices.