Of all periods of graphic design, my favorite has to be the early 20th century.  I love the use of color, and  the typography is just beautiful.  Recently I’ve found a nice source of inspiration in that vein at InternationalPoster.com where there is a huge collection of vintage posters searchable by subject, period, style, artist, etc.  They also have a very interesting history of poster art to peruse. Some of my favorite finds there:

 vintage poster 1

Artist: Mario Borgoni

vintage poster 2

Artist: Henry Le Monnier

vintage poster 3

Artist: unknown (hmmmm, maybe he went down with the ship)

vintage poster 4

Artist: Joseph Leyendecker

Artist: Antonius Molkenboer

What about you? What period of design most inspires you?