Just to add to your note about checking what an email looks like without images:

Be sure to include an "alt=" property in the image tag so that the user can see what the picture would be if they downloaded it. This will serve the dual purpose of making sure that any content that was image driven still gets across and also the reader will be more likely to allow the image once they know what it is, thereby allowing you to get open rate statistics.

Also it is important to include the height and width property in every image tag so that even if the image is suppressed your layout will be unaffected. If you fail to do this, Outlook will break your layout because they include a message about your the picture being suppressed that stretches the confines of the image if it is not restrained by height and width. That will break your layout and make the email hard to read for those that choose to keep the image suppressed.