WordPress.org

This plugin, Jayj Quicktag, allows you easily to add custom Quicktags to the post, page or a custom editor.

It adds a settings page where you can add all the Quicktags you want (see Screenshots)

It's uses the new WordPress 3.3 Quicktags changes so it won't work with older versions of WordPress.

It supports both import and export of your Quicktags so you easily can add them to another WordPress install.