I use
http://wordpress.org/extend/plugins/category-text/ on a couple blogs. I add recips and adds to specific categories. You can also chose to have it show on homepage or posts in that category as well.
I use category specific ads in each category and am happy with the plug in.
Only down side is that if you have a post listed in more than one category, it will show the "added text" from the listed categories to that post.