What PEB said... I would also add:
- MapMyRide (FREE): Great for finding road and off routes. Find what other may haver rode so you can repeat/follow. What I like about this one is the web site where you can download a gpx route and load it to your garmin gps to follow a route.
- MountainBike ($.99): Great if you travel and want to find mtb trails to ride. Equivalent of MTBR.com to find trails by city/state on your phone.