Zach Trenholm is one of the best caricaturists alive, and his depictions of the American Idol judges in today's LA Times is an example of why I believe that. With just a few lines, he completely captures the look and personality of the celebrities he draws.
Link to LA Times article about American Idol.
Link to Zach Trenholm's portfolio.
Draw! magazine, Vol 7, has an excellent interview with Zach Trenholm. The interview is not online, but you can order a back issue for $9 from the publisher.