GOG regularly holds a sale of the complete D&D series. Best to keep checking, as only GOG knows when, though I doubt it will go on sale again before the 25th, as you missed the last one just recently.

I'm so looking forward to this as well, but hasn't gotten that lower eveytime I checked. Still, here's to hoping :), since I can't actually spend the 25 or so bucks on the whole D&D pack, even though I own several already.

The "Hasbro D&D Bundle" (Hasbro being the publisher, as they own Wizards of the Coast, which owns the D&D brand) seems to go on sale at least a couple times a year, traditionally during the winter/Christmas sale (which is already finished). In the five and a half months I've been a GOG member, that bundle's gone on sale on three or four occasions, I'd say. (Here I'm counting two or more appearances of the bundle during any one major sale as "one occasion".) It last appeared (multiple times) during the Winter Sale which just finished up here early this past week, so I'd not count on seeing that bundle again till the new year (though you can hope).

I don't recall ever having seen any of those ten D&D games go on sale individually, so I'd just keep your eyes peeled for the bundle. Also, from what I've seen, the D&D bundle always has the same discount -- individual titles, or any combination of them short of the full roster of ones you don't own here, are 60% off; whereas the full bundle (ignoring any you already have) would be 80% off (21.10 USD for all ten).

If you REALLY must have it before Christmas, and don't want to pay full price, try asking around in one of the trading or gifting threads here. There may be someone who has a spare key they can trade to you (if you have something to offer which they want) or, if you're lucky, give to you.

Hope something here helps. :)