I use alot of costume stuff mainly my Rottweiler even though I am not a real fan of it either... I feel because of all the bad press Rottweilers get... anything to get the general public to realize that they are not child eating monsters can hopefully be a good thing. I do have to on occassion attempt to include my Airedale...

I find alot of my props at Michael's Craft Stores and iParty. They are usually cheaper than buying "pet specific" props. Michael's actually has really cute elf hats made in felt with chin straps that are really small for babies or little children, they may be great for small dogs and cats as well.