Basel
I just went to the Kunstmuseum in Basel, getting there at 7 p.m. To my surprise, I was told that they have a Happy Hour for the regular collection, so the entrance for the last hour of the day was free. Every first Sunday of the month is also free.
More info in English:
http://www.kunstmuseumbasel.ch/en/info.html
I quite liked the collection and its presentation - well, I am biased, because I had gone there to see Oskar Kokoschka's Windsbraut, and the way this particular painting is presented is impressive.
Idgie