Dorfromantik is a great one which was a big hit in Germany. Dunno if its widely known elsewhere but it should be, since it is a simple chilled coop Puzzler based on a cozy videogame.

The next two are not coop all the way but Mysterium and Treasure Island are pretty fun and invoke the same teamwork feeling around the table, if someone is content on beeing the GM.

In mysterium you have one person as a ghost, that sends visions to the other in form of abstract art cards, to find out how he died.

In the latter, one person plays Long John Silver and the other have to find his treasure on an Island (duh:), before he escapes prison and gets it himself.

It is meant to be played against each other, but if you tweak the rules a bit is very nice as a coop experience. Especially for kids, since you can draw on the whole map to mark down places that you rule out. Very nice family game for all ages.