Simpsons merchandise, such as the excellent Simpsons comics from Bongo and Inkworks' Simpsons trading cards, continue to mirror the long-lived popularity of the series, although the long-running Playmates Simpsons Toys may have 'jumped the shark' to some extent around Series #10. Playmates has done a good job of keeping The Simpsons toys fresh by adding in new versions of the major characters, but exceptionally long-running toy series like The Simpsons or the original Playmates Teenage Mutant Ninja Turtles figures eventually hit a wall of 'collector fatigue' brought on by lack of storage and display space -- and this kind of problem can have more of an effect in specialty stores that cater to collectors than it does in the mass market, where new potential audience of kids starts watching The Simpsons every year.
Meanwhile King of the Hill merchandise, which started off slow as a Texas drawl, has grown to include its first series of action figures, which just arrived from Toycom during this year (King of the Hill's seventh season on the air). Both The Simpsons and King of the Hill are also in widespread syndication around the country, which raises their visibility considerably.