The most memorable, most fun costume I ever made for my 2 year old son was also the simplest and cheapest.  And he got more compliments than any costume since!  I went to a thrift store and bought a camouflage shirt that was too big for him (so it was almost like a dress).  I then bought several packs of fake fall leaves that were on clearance at Michael's.  I hot glued the leaves all over the shirt.  Then I dressed in flannel and overalls and carried a rake.  He was my "pile of leaves".  He was very comfortable because I could dress him warmly under the costume without covering the costume, and there were no masks, face paint, etc. to mess with.  An added benefit to the evening of trick-or-treating as a pile of leaves...getting to "hide" in real piles of leaves and making mommy find him.  We had a lot of fun and I spent all of about $4 total.

-- Lori F.