One thats a favorite of mine that I dont think was mentioned is Cats and Dogs...even though they portray cats as "evil" (wouldn't you be after getting treated the way that poor cat got treated lol )

I love All Dogs Go to Heaven (the ending still makes me cry though), Milo and Otis, the Incredible Journey (the original) and 101 Dalmations (the sequels...ugh lol)
White Fang and Call of the Wild are good too, but the books are better IMO lol. Balto is another good movie, but if you enjoy the movie I reccomend reading about the real life Balto
My husband says that the Never Ending Story should be concidered a dog movie because the luck dragon looks like a big flying dog (now that I think about it, since when do dragons have fur?)

Heck I think Ive enjoyed just about every movie Ive seen about dogs although they have a history of making reeeeeeally cruddy sequels (Air Bud and Beethoven come to mind)

And I have to vote for Best in Show as one of the funniest movies ever. I need to go watch that again lol.