Serge Gainsbourg appeared in quite a few commercials back in the day, there are a few on Youtube and other video sites like this one, this one and NOT this one. Probably the most famous ad he did was for Black & White whiskey. Here you can also download a song Serge and Jane made for after shave brand Caron. (Thanks Anna) EDIT: The Perrier-commercial was not made by Serge (see the comments). I googled some more, and found this one, probably the best commercial EVER with Serge in it (if you don’t get the joke, see this).
In other Gainsbourg-related news: meet Benjamin Paulin, who styled the cover of his first album after Serge’s debut-EP. His music refers to Leonard Cohen, MC Solaar and Serge of course. I’m crazy about the long (7 minutes) title track, that sounds like an updated inedit of Melody Nelson. See more here.