When I was in Poland I went to the poster museum in Wilanow. They had a rather small exhibition as apparently there was some sort of radiator emergency in the other gallery, but they were displaying some work by Stefan Norblin, an early 20th century painter, illustrator and designer. The gallery showed a range of his broad portfolio which ranged to everything from posters to periodical covers to portraits. He even did a bit of costume design so there were some costume sketches on display. I particularly like his art deco/modernist posters. Unfortunately I can't seem to find certain images online, so some of these are poor quality snapshots taken with my phone, but I thought the illustration with the windmill (presumably Don Quijote) and the oval shaped art noveau life drawings.
The museum itself is pretty cool and has had some great exhibitions in the past, some of which are archived on their website. I really like the Polish travel poster exhibition.