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.).

darrinb

Easily include raw markup languages (HTML, CSS, PHP, etc.) in comments using custom quicktags. No need to encode, the filter does it for you. Creates convenient “encode” buttons for comment authors in the HTML editor.
Also adds basic quicktag buttons on the comment forms, using the Quicktag API built into WordPress (as of 3.3).

David’s Ultra Quicktags vs WP Comment Encode