Don't forget that September is the month when the major retailers of wine in France try to outdo each other with the reductions they offer. And you no longer have to live in or go to France to profit from all this discounting. All the main French online retailers also take part nowadays.
The most comprehensive guide to the best deals chez each retailer that I know is the September issue of La Revue du Vin de France which I commend for cool, calm study before committing any cash. RVF gives the precise dates of each retailers' promotion (they all vary) as well as which they reckon are the best buys and in most cases a rating of their range, prices and 'originality'. Of the big supermarkets, Geant Casino wins top marks for low prices and a pretty good rating for the other two aspects too.
Of online retailers, wineandco.com is said to have 'la plus belle offre sur Internet' 1855.com (oft discussed without great enthusiasm on our forum such as here) is not rated but is reported to have discounts of up to 40% as part of its fourth annual Crazy Bordeaux promotion. Chateauonline.com (also discussed with some frustration on our forum, although not recently) gets fairly high ratings too.
It is worth noting that there are lots of 2005s in the RVI selections (quite how many bottles are actually on offer is another thing altogether). Vintages 2004 and 2006 probably make up the bulk of the merchandise, I would guess, although there are a few older vintages to keep things interesting.
Happy hunting, but do please read the small print, and preferably all those threads on our forum (click on the arrows next to Topic to put them in alphabetical order and find 1855.com easily) if you are ordering online.