I recently saw mention of a Mac IIsi memory hack project and that got me thinking of possible upgrades for my IIsi.
When I first picked it up about two years ago I installed an FPU and upgraded the video card to a Supermac Spectrum 24 PDQ+ 24 Bit.
The RAM is only at 16MB so I could definitely upgrade that. To be honest, I am hoping to find something a bit more exotic. The Radius Rocket was suggested earlier - I'll be keeping my eye out for that.