Folder Structure

/AppName
    /Shared
        /Application      # App delegate and related files
        /Controllers      # Base view controllers
        /Models           # Models, Core Data schema etc
        /Views            # Shared views
        /Library          # Anything that falls outside of the MVC pattern
        /Support          # Categories and helpers
    /iPhone
        ...               # Same structure as 'Shared' but with interface specific classes
    /iPad
        ...
    /Other sources        # Prefix headers, main.m
    /Supporting files     # Info.plist
/Resources                # Images, videos, .strings files
/Vendor                   # 3rd party dependencies not managed by CocoaPods

Credit to Sebastian Rehnby for the layout.