And pedals! I've half-seriously considered experimenting with an expression pedal as a vertical scroll controller for desktop applications, using a second pedal to switch between relative (pedal position relative to center → scroll velocity, zero movement when pedal position is centered) and absolute (pedal position → page position, zero movement unless pedal position changes) modes.

For wide multicolumn IDE/text-editor layouts, spatially-mapped fader banks and/or organ drawbars might also make useful scrollers.