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.).

Marc Tönsing

Ipstenu (Mika Epstein)

This plugin displays the most basic of quicktag buttons on your comment forms, using the Quicktag API built into WordPress (as of 3.3). No jQuery needed.
Contribute on <a href="https://github.com/mtoensing/marctv-quicktags" rel="nofollow ugc">GitHub</a>.

Simple Comment Quicktags

Simple and clean

Make commenting easier with bold, italic, add link and quote buttons on top of the form.

David’s Ultra Quicktags vs Simple Comment Quicktags