iTouch
The iPod Touch can run all the applications and connects through wifi, which can be picked up at quite a few airfields. I use:
AeroWeather - excellent as already mentioned
Pilot Wizz - good for weight & balance etc. only need a connection for weather.
GeeMeter - measured + and -ve G, just out of curiosity.
Without the phone connection, I also use WiFinder to find the free open networks.
All the above are free apps.