What's a good sports tracker app for iPhone? I'm looking for an app for tracking activities like walking, running or bicycling. Lots of people I know with Android or Nokia phones use such apps, but I don't know what's a good option for iOS.

Requirements:


Can track time &amp; distance covered (using GPS)
Should be very simple to use: 1) start the tracker 2) go for the walk/run/ride 3) stop the tracker and see the distance &amp; time
Available on App Store (i.e. works on non-jailbroken devices)


Preferably free, but feel free to recommend an excellent paid app too if you know of one.

Also, it's a plus if I can use the app for my simple needs without signing up to any service.
There are a number of them in the App Store that meet your criteria.  Here are the ones I've used:


Strava.  This app motivates people into exercising harder by bringing out their competitive side.  With Strava, you can compare your times with others who've done the same route.  This app is most useful when you workout in a group where you'll be able to push each other.
Runkeeper.  The unique feature of this app is in its "coaching".  Basically, if you like to change your pace at certain intervals, the app can notify you when to switch.  Additionally, this app can pair to a heartrate monitor.
MapMyRun.  This one tries to be your overall fitness app where you can also log your caloric intake and other activities such as weightlifting.


They are all good options depending on your specific needs.  Try them all and see one fits you best.  Have fun!