I’m not sure what would best suit the attendees or what others are covering, so I’d be happy to cover one (or more if I can do a 40-min talk) of the following:

• icon design with a HowTo or demonstration of how to design and icon [1];
• website design — setting up a grid, laying down the various page elements for a graphical mockup of a website [2];
• web app mockups — designing web applications mockups [3];
• clip art — doing it, dissecting an existing clip art piece and submitting it to OpenClipArt.com [4].

Example pieces that might work for each presentation: