In no particular order...
A search engine ... for my house.
A hovercraft option in my car, for escaping traffic jams.
A camera, preferably with video/audio, attached directly to my head, so I can capture the awesome moments with my kids that I see, but that end before I can grab my camera, and which cannot be replicated.
A device that cuts kids' fingernails perfectly & painlessly and alerts me before their nails reach talon status.