Download WP Function Lookup For Alfred v2 Only.
Usage
> wp function name
If there is a function name match, choose to view to open the Codex page, the file it’s defined in on phpXref, or the QueryPosts.com page. If no match, search the Codex.
When an item is selected, the URL will open in your default browser.
You can download Alfred App for free here: http://www.alfredapp.com/.
To kick things up a notch with extensions and more, get the Powerpack for Alfred.