I managed to do almost all my christmas shopping in Paris before heading home. I was actually quite sick but I did enjoy strolling along a lot in christmas decorated streets and stores. And taking pictures of it all (naturally).
You just have to visit Merci if you're in town and in Marais, love that shop! Very Merci-ish decorated for christmas of course.
The Conran shop, just by Bon Marché near Saint German, is well worth a visit as well. Gadget and gift heaven!
And next door to Le Bon Marché is La Grande Épicerie, aka The Greatest Foodstore There Ever Was.