For anyone with pre CAAD4 Cannondale frames (earlier than 2005) this is quite an excellent resource:
Vintage Cannondale - Information and Catalogs for Cannondales
Has information on serial numbers, logos, parts catalogues, Cannondale catalogues in pdf format dating back to 1974 and even has a nice gallery full of 'Dales for your viewing pleasure. It’s basically an online resource centre for Cannondales.