Leonardo da Vinci [Public domain], via Wikimedia Commons (cut)
I’m currently listening to a presentation by Prof. Martin Eppler about “Sketching at Work” — showing the power of sketches in business contexts. Sketching is a very powerful tool in creativity and as far as I can see, his book (look into it) or here (order) offers a lot of ideas how you can use sketching to solve and discuss your problems.
Very interesting book and I agree, now that we have tools like the iPad that allow sketching (esp. if you use pens like the Pogo sketch pen) sketching is back.
Very interesting 
P.S.: If you like to look at presentations which work heavily with sketches, look at the presentations at Khan Academy or (more professionally) the RSA Animate videos.