I've been using the Noun Project this term with students to produce infographics. Text and simple images are apparently useful to help students remember because of the visual cue that they provide.
The Noun Project promises 'icons for everything' and these can be downloaded for free under CC license.
We've been using them to produce what we call a 'Little Book of Cold' - to explain why Antarctica is so cold. Icons can be downloaded with a free account, or customised.
The Iconathon is an extension of this, where designers get together to develop icons around a theme. The DISASTERS set is a good one to use, for example.