Even older is Laurel & Hardy "The live Ghost" (1934).. It still cracks me up
http://www.veoh.com/watch/v20252983hSKzBQ7n?h1=Laurel+and+Hardy+-+The+Live+Ghost
http://www.veoh.com/watch/v20252983hSKzBQ7n?h1=Laurel+and+Hardy+-+The+Live+Ghost
Abbott and Costello Meet Frankenstein....LOL
I can't pick just one. So I will have to say the first horror movie I saw as a kid. The original Dracula.