The best place to start your search for Iditarod-related lesson plans in on the Iditarod Education Portal. There you will find lesson plans arranged by subject area. The Iditarod Education Portal includes lessons for math, science, social studies, and language arts. Take a look at this lesson (link opens a PDF) about friction to get a sense of the kind of lesson plans that you will find through the Iditarod Education Portal.
Scholastic offers a nice collection of materials about the Iditarod. Included in those materials is an interview with author Gary Paulsen in which he answers questions based on his experience in the race. The Scholastic Iditarod resources also include some history of the race and history of Alaska in general.
The Discovery Channel offers 37 video clips related to the Iditarod race. The clips cover information about the dogs, the mushers, the sleds, and the history of the race.
For your students who are interested in learning about the dogs used to pull the sleds over the 1100 mile Iditarod course, the American Kennel Club is a good place to find information about Alaskan Malamutes and Siberian Huskies. I should note that most of the dogs that run in the race aren't pure-bred dogs. I've met many mushers and one of my former colleagues is a musher (not in the Iditarod) whose teams that aren't what you might expect to see when you think of sled dogs. To learn about genetics and breeding of dogs I recommend National Geographic's article How to Build a Dog.
The From Alaska Educational Program has five pre-made units of study about mushing (dog sledding). Each unit has articles, images, and quizzes about mushing. Three of the units also include video and audio clips.
Snag Films hosts a couple of videos that may fit with your lessons on dogs too. The Nature of Things: Man and Dog is a 45 minute video about the relationship between humans and dogs and how that relationship has evolved over time. Dog Bless You is a five minute video about the first no-kill homeless dog shelter in Idaho. As someone who has two rescued dogs at home, I have a special affinity for Dog Bless You.
A special note about this post.
I write a post about the Iditarod every year and every year I receive critical comments about my decision to do so. As mentioned above I have worked with a musher and met many others over the last few years. I've seen how well those dogs are cared for and how much money those mushers spend on the care of their teams. I am very comfortable in saying that sled dog racing is not cruel to the animals. If I didn't believe that, I wouldn't post about the race. I also volunteer at a no-kill animal shelter and have rescued dogs myself, I wouldn't promote something that I thought endangered dogs