This plugin adds up to four new buttons / links to the WordPress Editor panel. You can select to add a quicktag to easily insert: 
Amazon item links 
Amazon product searches 
custom span class 
custom div class
The settings pane allows you to enter defaults, as well as your own Amazon associate ID.

David’s Ultra Quicktags

Adds new buttons to the Editor window (Amazon Links, Amazon Search, etc.).

Jesper Johansen (jayjdk)

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

Jayj Quicktag

Allows you easily to add custom Quicktags to the post editor.

David’s Ultra Quicktags vs Jayj Quicktag