Slide:ology has a recent post giving useful advice on how to use maps in your slides. The post has stimulated comments that have some more useful tips from people's experience. Slide:ology plan a Part 2 to this post.
They mention the guru of informational design and visual literacy, Edward Tufte. If you really want to get into this side of creating sides, he is a stimulating read. I find his books quite demanding to follow, but The New York Times described Tufte as 'The Leonardo Da Vinci of data'