The latest issue of the free online journal, Evolution: Education & Outreach, highlights transitional fossils.  There are several good articles here: I especially liked Jenny Clack’s piece on the fish-to-reptile transition, which is now documented by many more fossils than just the famous Tiktaalik, and Thewissen et al.’s article on the evolution of whales from terrestrial mammals. The articles have nice figures for teaching purposes. This is a great journal for laypeople and scientists alike to keep up with education in evolutionary biology, and it’s free.