Morgan Kay

If you use a service such as Feedburner or MailChimp to turn your RSS feed into an email subscription, and the images in your posts are more than 600px wide, the formatting of your HTML emails might be messed up. This plugin lets you resize the images in your RSS feeds.
Version 2.0 has been completely re-written from scratch! It is now more reliable, and works with images from external URLs.

RSS Image Resize

Resize images in RSS feeds so they will fit in HTML emails.

alaingg

Simple plugin that allows to include the images into your wordpress rss, rss2. 
The plugin use the post/page thumbnail or the firt attached image to the post/page gallery. viste the <a href="http://web-argument.com/2008/11/09/wp-rss-images-wordpress-plugin/" rel="nofollow ugc">plugin page</a> for details.

RSS Image Resize vs WP RSS Images