Garmin FORETREX 101 GPS Receiver

Well, not perfect, but by far the best small GPS.
The wrist strap is small and bulky. Just replace it with a normal sports watch strap.

Uses 2 normal AAA batteries - even the high capacity NiMH (important if you need more battery power and no-place near a charger or factory service!). No external device required. It works. You CAN connect to a PC/Mac via Serial/USB and get your position on mapping software, COOL.

Bulky for a watch, but still the smallest GPS with normal batteries you can find. No maps, but the small device has a small screen and you get to where you need to go anyway.