A footer slider (also known by other names) is just a pop up footer that allows users to see an ad or possibly subscribe to an email newsletter. Nobody likes ads, but in a ministry context you could use one to promote an event or invite people to subscribe to an email newsletter for the church or even the church blog (through Feedburner Email Subscriptions). You can see one in action on the Church Leader Insights website, which allows users to subscribe to their newsletter.
I recently had a client want one on their site for the same purpose and thought you might want to know what I used. I could not find a great plugin that made a footer slider and allowed for customization. I ended up using the AWeber Footer SlideUp plugin. AWeber is email marketing software but I simply edited the main plugin file (awfs.php) to put my own form information in there and I edited the included CSS file (style.css) to make it match the look of the site. It worked out very well.
