Lux – If you like the table game Risk you will love this. There is a free version with one map, the payed version has more.
MultiConvert – Converts anything I can think of
Currency – If you buy a lot of stuff from foreign web shops…
Clinometer (costs money) – If you want to measure stuff like a bikes head angle or how straight some surface is
I just installed Everytrail and GPS LTE which I believe can record gps data for a bike ride and them map it out in google maps / give statistics on the ride (elevation, speed, destination etc). Did not have a chance to test them yet.
Other fairly nice games:
Geared, Drawrace, Flightcontrol (all cost money)
My kid likes these games:
Jelly Car, PapiJump, PapiMissile, Topple, AlpineCrawler