Finding an Ad Management System?

aagha asks: "I'm working for a very small, three-person startup in Athens, Greece (with a dwindling budget), trying to create the first real, full-featured tourism website for this country. While we have our home-grown Java-based Content Management System up and running and our site working fairly smoothly, we're having one heck of a time finding an ad management system to to work with our system. We have URL's which contain params to build our pages dynamically and we can't find a solution to work with our JSP's to serve ads targeted by category and or article. I know that I'm not the only person writing software for a JSP site (uhhh, or am I?). I'm curious to know what others have done to meet their advertisement serving needs."