AppKiDo is a free ReferenceTool for Cocoa Objective-C programmers. The goal of AppKiDo is to help you find what you want in the Cocoa documentation. It does this by parsing the header files and the HTML doc files that were installed with your Developer Tools, and presenting the results in a form that is easy to navigate. More info:

http://homepage.mac.com/aglee/downloads/

The most recent version supports Leopard.