Apps for walking

I have Runkeeper. Keeps track of lots of activities.

Fit bit
Endomondo

I also have Pedometer. Check it out, it's cool!

I use Runkeeper.

Short answer: Runkeeper.

Long answer -- here are the fitness apps I've got on my iPhone:
- MFP Calorie Counter, which goes without saying;
- FitBit, too be honest kinda lame since it's not real-time data and only relects the last time you synced your FitBit with your computer (they really need a Bluetooth Smart Ready version of the FitBit that can sync directly to the phone);
- Runkeeper for walks, hikes, runs which is awesome! I also use it to manually track elliptical;
- MapMyHike for hikes;
- Seconds Pro interval timer, nice because you can match music to the fast & slow parts of the workout;
- Withings WiScale, so I can see those cool graphs on my phone of my weight & body fat (weigh myself before my first cup of coffee, and not have to check what my weight was until after my first cup of coffee! Priceless!
- TwoHundredSitups, so I can do the challenge!
- Hundred Pushups, same folks as the Situps app;
- JEFIT, for strength training, keeps track of the weights & reps.