Mobile PC has compiled a list. Here is how they define gadget:
What defines a “gadget” anyway?
* It has to have electronic and/or moving parts of some kind. Scissors count, but the knife does not.
* It has to be a self-contained apparatus that can be used on its own, not a subset of another device. The flashlight counts; the light bulb does not. The notebook counts, but the hard drive doesn’t.
* It has to be smaller than the proverbial bread box. This is the most flexible of the categories, since gadgets have gotten inexorably smaller over time. But in general we included only items that were potentially mobile: The Dustbuster counts; the vacuum cleaner doesn’t.
The top 5:
1. APPLE POWERBOOK 100, 1991
2. ZENITH SPACE COMMAND TV REMOTE CONTROL, 1956
3. SONY WALKMAN, 1979
4. MOTOROLA STARTAC, 1996
5. CDI MECHANICAL MOUSE MODEL 4-101, 1970