I generally like to plan based on input from a variety of sources (guide books, magazine articles, travel sites, friends who recently took the same trip, etc.) Gathering all that information is great but I've sometimes wished for an efficient way to access and sort those recommendations when I need them most - while I'm out walking around - rather then in my hotel room.

New York's public radio station, WNYC, recently revamped its app to incorporate this feature, which I agree is very useful:

http://www.wnyc.org/mobile/

A lot of the available content categories aren't specific to New York, so it might be worth checking out regardless of where you live.