The Lost Art of Cassette Design by Steve. I remember spending hours hitting "play+record" making mix tapes & drawing the sleeves during the tracks. A well planned & decorated tape was always gratefully received by your mates.
Some good basic introduction info from Crutchfield. Crutchfield outlines some common features and options that you'll come across when you shop, and what they mean so you can decide which ones best fit your needs.