Recommendations for 1930s-1960s vocal jazz a la Serge Gainsbourg's first few albums
 

Something like these:
http://www.youtube.com/watch?v=StI_p567_NE
http://www.youtube.com/watch?v=ZGE1-JiiqVU

I'm not really interested in his later experimental stuff, but more artists/performers in line with the chanson style. It also doesn't have to be in French, necessarily

Charles Trenet would be an obvious one to begin with.

I don't know if Cora Vaucaire fits the bill but I loves it anyways.