My instinct is to go to a visual dictionary or wikipedia and get ideas there.
... [snip...looking forward to your presentations :-) ]
A concern I have is that some of these topics are just not suited to flat computer presentations...isn't it important to get all 5 or your senses involved for many subjects?
Well, as I see it, presentations in the 21st century, with the help of the Internet, are a brilliant way to show
pictures and thereby visually teach concepts. Other senses are important too but for my money, words and pictures are far and away the most important. Obviously, you can't teach some concepts with just pictures (like "rough" or "loud") but you can reinforce even those...
As to a visual dictionary, well, absolutely. We've got several. Excellent source of ideas for presentations. We still read the Oxford Picture Dictionary, we've been going through it slowly but steadily for over a year now, now we're past page 180 I think, and finally in the last 1/3 or so of the book.