An introduction to Bitcoin I gave at BarCamp Nottingham on 23-July-2011. Blog post here: http://aviewfromafar.net/the-barcampers-guide-to-bitcoin
Note: I've updated this! The new version is just called "Introduction to Bitcoin", and is here: http://www.slideshare.net/ashmoran/introduction-to-bitcoin-30852714
Clipping is a handy way to collect important slides you want to go back to later.