By the way, they are keeping track of the games on sale on Reddit. Here's the list so far:
http://www.reddit.com/r/GameDeals/comments/1wdc1d/gog_drm_free_time_machine_sale_time_limited_deals/
1983. Zork Anthology, $1.79/70%
1984. Ultima 1+2+3, $1.49/75%
1985. King's Quest 1+2+3, $2.99/70%...