There are many apps (like RunKeeper and RunMeter) that track where and how much you run, but not many to help you discover new places to run. Luckily, there's the WalkJogRun app [iTunes link] ($.99US), which gives you the ability to navigate through over 500,000 user-submitted map-based running trails.
The iPhone app shares much in common with its desktop browser counterpart. Like WalkJogRun.net, the WalkJogRun app allows you to view specific running trails that you've created, as well as those created by others specific to a certain address, city or landmark (i.e., Golden Gate Bridge, MGM Grand Hotel, etc.). But iPhone technologies provide new layers of functionality and interaction lacking on the site, such as geolocation for finding nearby running routes, which I find very useful in areas I'm not familiar with, and the niceties that come with navigating a map with the iPhone's multitouch display.
Nonetheless, the WalkJogRun app could use some improving. The most needed improvement is the ability to save or bookmark a running trail, which one can do via WalkJogRun.net but not on the iPhone app. My workaround for this is to take screenshots of running trails that I like in the event that I navigate away from the map and can't remember the name or location of the trail. Another improvement, though more of a "nice to have" than a "must have", is the ability to create a trail on the iPhone.
These things aside, at its USD $.99 price tag, the WalkJogRun app serves as an ideal complement to GPS-based iPhone running and biking apps, as well as the Nike+ kit.