Here's a video I came across about Charles N. Landon, the founder of the Landon School of Illustration and Cartooning.
I have a bunch of correspondence course books including "Cartooning for Profit by David Rand" and the "Cartoonists Exchange Presents...Paul Robinson's Post Graduate Course".
They are a little outdated, but there is still a lot of valuable information in them. You can usually find them pretty cheap on eBay. If you are interested in these type of courses, especially their history, you should purchase this upcoming book from Rick Marshal titled, "Mail Order Geniuses".
Speaking of how-to cartooning books, Mike Lynch over at Mike Lynch Cartoons is offering his own cartooning books. Mike's books have been so popular that they sold out and have had to be reprinted. He is now offering them as a set which includes an original sketch for only $7.00. That's cheap! Go here to purchase them.
Tom Richmond, caricaturist and illustrator extraordinaire has a book coming out next month called "The Mad Art of Caricature: A Serious Guide to Drawing Funny Faces". I've been looking forward to this book for some time now and it looks like it will be ready to order on July 21st. Go check out Tom's blog to see a preview of the cover.