1) My Fitness Pal, no need to say anything else
2) My Tracks, Googles GPS app to track where your going. I used this on my Droid Eris and it just wasn't that good. It could have been my location or my phone but that app just didn't work well for me.
3) Noom CardioTrainer, I used this app for 6-8 months on my Droid Eris. When I used the free app there wasn't much to it other then it would keep track of your workouts and total miles. That's all I used it for. From Google Earth and driving our street, it was by far the most accurate GPS app for me. Simple to the point and since I was only walking when I used it got the job done.
4) Sports Tracker, only used it for 1 or 2 walks. Like the user interface but it was way off on distance. This was also with my Eris which wasn't the greatest phone.
5) Endomondo Sports Tracker, I really liked its user interface and all the extra little things it did. I did use this for a little bit but when I upgraded to my Nexus it didn't work right off the bat. Overall this is a solid app but I fell in love with another app.
6) Map My Run, Once my brother showed me (Map My Ride) I was hooked. Map My Walk/Run/Ride are all the same basic apps (I think) and you can change what exercise your doing before you start a workout. This has been by far the most accurate distance wise and the calorie burn for my runs are not far off what my HRM says. Where this app excels at is its website. I can go on and on but its one of those you just have to check out for yourself. One key feature of the site is that you can create a course. It pulls up Google Maps and allows you click away on the map to create a course. It will tell you how far you have gone and has a few options on how to create it. I have used this to help me figure out where to go on my long runs and bike rides. You can save the routes and even search other users submitted routes. This is all done on www.MapMyFitness.com Since I started using this app, I haven't even looked into the other apps listed above or even sought out new ones. This app seems to do everything I need and more.
7) C25K, The Guy Hoffman Couch to 5K, This is a great app that helps you go from walking to running 30 mins straight. While its called C25K, I have yet to run a 5K in 30 mins. lol The idea for the app is to get your body used to running. It slowly builds up the running over time till you are able to jog 30 mins straight. If your new to jogging and need a little structure, hands down the best app to use.
I know there are GOBS more out there, but these are most of what I've used getting started. The nice thing is these are all free. Download them and try them out. Don't like it, delete and try another. As long as your moving, that's all that matters.