I'm not sure if there is already a plugin for this, but here is what I would love to have (but don't know how to do/implement).
If you go to my site, ProjecTech, you will see that I have the menu on the left-hand side of my site. Well, I would love to be able to have ads (selected by admin) display underneath my last list ("Links"). If anyone could do this, I would greatly appreciate it.
Also, if you could implement a few other features: (1) controlled by admin only, (2) choose ads from a folder and where they link to, (3) choose what pages the ads would display on (maybe, which categories the ads would display on).