iPhone without a shadow of a doubt. Even my wife was sceptical when I bought it;
A few weeks back we're out having a coffee in Bolton, we got chatting about changing the gas fire and putting in a wood burner in the living room. Within a few minutes I had found 3 places not far that did them, phoned one to find out if they we're open (was a Sunday), plotted the route on google maps, and set off, wife directed me to the place as she could watch us travel down the road to the place.
I think the phone was worth it just for the application called Shazam.