Custom sidebar widget for each post I write

I run a gaming website, redbarrels.net, on which I post roughly 5 articles per week. Currently, I use my Amazon Affiliate membership to display a single text widget in the sidebar (using the code generated at Amazon to display one of their widgets, which I update periodically) and I add a couple of text links into most articles (when they’re relevant).

What I would like is to have a different Amazon widget, which relates to the content of the post (so if I’m writing about Assassin’s Creed, I can have a custom widget linking to it on the various formats), on each post that I write. Ideally a plugin which adds a field to the ‘Write post’ screen into which I can post the custom widget code generated on Amazon and have that used to display the widget on the side bar when that post is visited. There would also need to be a ‘default’ widget to be used on non-post pages.

I’ve searched through the forums and the plugins, but can’t find anything that matches my criteria, is there anything out there?