As an experiment, I've added a new feature to the site. Scroll WAY to the bottom, and you'll find a list of "labels." These are tags that I add to each post to indicate the appearance of a particular character, setting, or subject matter. Clicking on one of these labels will pull up all the posts with that label.
So you can easily find all the cartoons that feature the Penguin, or Doctor Coldblood, or Dinosaurs, or even Thunderburger, just as examples.
I don't like the way this is formatted, but the list is so long I think it would be even worse in the sidebar. Give it a try, and let me know what you think.