Dash 2 (note: paid app) has just been released and it comes with a Alfred 2 Workflow. Dash lets users instantly search through documentation for 130+ APIs (ranging from HTML to Cocoa), for more information, check out Dash's webpage. All of the Dash-supported documentation sets are available for offline use.
You can get the Dash workflow by installing Dash and going to Preferences > Integration > Alfred.
Supported documentation as of the 2.0 release (documentation is constantly added so this list might go out of date): iOS, OS X, Man Pages, .NET Framework, ActionScript, Akk