If you’re looking for some inspiration, the Bostom Public Library has a fantastic Flickr account with lots of classic posters. They’re all licensed under Creative Commons and for available at a reasonable size (unlike many similar resources).
I really love the style of these old travel posters. The colours they’ve used and the hand-painted texture gives them a lot of character that is often difficult to reproduce digitally. The scans, with their subtle paper texture, creases and folds, only add to that. I particularly like the layers of colour in the poster for ‘Motoring in Germany‘.
As well as the travel posters, there are WWI and WWII propaganda posters, old manuscripts, postcards and photos. The whole account is a great resource for colour, texture and general design inspiration.












