I do it all manually. Prefer it that way. There is a plugin here. http://manalang.com/wp-amazon New version pending for WP 2.1
My friend was just developed it At this present, it's on stage of trial and error I am waiting it as well ^_^
You should take a look at Triggit its a web application that makes it super easy to add Amazon links into your wordpress blog. Certainly worth a look. Shoemoney wrote a post about it here: http://www.shoemoney.com/2008/01/17/triggit-the-bloggers-new-best-friend/
I currently have a Wordpress Plugin in development. A little more about it can be found here: http://developedat.com/?p=6
Try to search in here http://wordpress.org/search/amazon I found plenty of plugins that might help you a lot, I use a Plugins from WordPress Widgets. Have fun
http://forums.digitalpoint.com/showthread.php?t=784143 < there is one here that turns ISBN's into Amazon affiliate links. very simple and effect
I would like to announce Amazon RSS in Wordpress. Ioncube is needed for this Wordpress plugin to work.
No; I don't have a demo site for the administrative back end. However, you can see the plugin in action by looking for the images after the blog post on my site. However, I do have screen shots of what the admin menu looks like on my flickr account.
I've tried many and in the end I end up paying for one that is well worth it. Reviewazon.com. I am not affiliate with them and I don't regret buying it one bit.