The best visual aids are a kind of shorthand. Charts and illustrations are the visual aids used most commonly and effectively by the creators of slides, transparencies, and flip charts.
Charts are inherently flexible and can show graphs (bar, pie, or line), organizational relationships, cause and effect, and how one event relates to another (flow chart). It's up to your imagination. Whether a diagram, cartoon, map, or original artwork, illustrations make visual aids visual and keep them from looking like typed restatements of your speech.