Apple's [science page](http://www.apple.com/science/) has a collection of [Keynote templates](http://www.apple.com/science/poster/WWDC_Poster_Templates.zip). They even have a [short video](http://www.apple.com/science/productivitylab/#tutorial=researchposter) about using the templates. (OK, 3D marble bar graphs are probably not the best, but you were going to make your graphics in IDL and import them anyway, right?)
UPDATE 10/27/12: Apple seems to have removed templates, here is a [cache].
[cache]: http://michaelgalloy.com/wp-content/uploads/2012/10/WWDC_Poster_Templates.zip "WWDC poster templates"