I know many others have linked to it already, but this mashup video, "Right Wing Radio Duck" -- where Donald's unemployment and economic insecurity make him receptive to the Glenn Beck show -- is today's viral video, and rightly. The creators deserve some kind of prize for finding a way to tell a complete, coherent story with almost nothing but actual Donald Duck cartoon clips and actual radio voice-overs.
It's been a while since I watched a lot of Donald cartoons, so I'm not sure, for the most part, which clips the clips come from (except for the obvious ones like "Der Fuehrer's Face," a few clips from "Window Cleaners," and the José Carioca bits). Maybe someone will put together a list of sources.
Update: As pointed out in comments, I originally confused José, who is not used in this cartoon, with Panchito Pistoles, who is. Maybe José can be saved for the sequel about Donald confronting the Brazilian menace and the secret Stalinist plot behind FDR's nefarious Good Neighbor Policy.