I use:
* The Hundred Pushup challenge, to force me to do pushups 3x a week
* Fitbit, to keep track of my daily steps
I used to use RunKeeper and Couch25k, but had to stop running so haven't used those in a while.
I was skeptical of fitness apps, but they've turned out to be pretty useful! I may start logging my intake with MyFitnessPal...
Do you use any fitness apps?