This is one of my favorites from parents.com - a cute, simple, and warm kitty costume! It was from a submission for an article on "Costumes Made By Real Moms."
Here's a link to the article: http://www.parents.com/holiday/halloween/costumes/halloween-costumes-made-by-moms/?page=18
Instructions: Cut the boa into five lengths: two to go around the ankles of the pants, two around the wrists, and one more to go around the neck of the turtleneck. Glue the boa pieces in place with fabric glue. Cut out ear shapes from the felt. Glue them to the hat and add a few feathers inside each ear, keeping them in place with glue. Glue felt tail to the back of the pants.