Multiple single-post templates

Spent the better part of the afternoon trying to figure this out, and I surrender! Here’s my quandry:

What I would like to do is have multiple ways to display a single post, depending on what category the post falls into. For example, a blog entry with lots of text would have a different layout than a blog entry with a single photo. Setting up two different categories is not the problem… it’s the fact that they appear to use the same single.php file.

I’m just not finding what I’m looking for in any of the documentation, so if someone can point me in the right direction, I would be most appreciative.