My serious thought mirrors alphanstein's: a good universal DVD player, possibly with DVI and/or HDMI output. The market for such a player has actually grown a bit since some of the major player makers have moved more toward the mass market design approach. I briefly considered a good universal remote for this one, but I think that Home Theater Master and Harmony have done a lot to fill that need.

A more entertaining thought: "cabinet wiring gnomes" - extended tools (or perhaps really well trained chipmunks) that can reach behind an equipment rack and allow you to make all of your wiring connections without having to twist yourself into a pretzel. They could even be sold in a specially-priced bundle with a case of PCA interconnects.