BetterKeyBinding

From WoWWiki

This AddOn provides a better key binding interface and user experience. Instead of built-in WoW behavior of changing a key binding and then telling you that it was previously in use (and you then having to go find the previous binding and re-bind it) this addon instead warns you of the previous use and then allows you to click a "confirm" button before committing to the change. There is also a table of section headers that allow you to jump directly to specific sections in the list of key bindings.