Excellent thread, thanks for starting it !
For those of you who happen to visit Singapore (riding or not), check out iMerlion. It's an app directory of all apps Singapore related. Perfect to find your way around, and make the best of your visit with your iPhone. Most of these apps are free.
For the Singapore riders, Weather Lah is a must have to check the latest on rain forecast before taking off
Ride tracking/logging apps are the ones I feel we miss the most - anyone stumbled upon some new ones lately ?