March Madness Non-D&D Blog Challenge: Day 29: What OSR product have you enjoyed most?

This would the Desert of Desolation modules for AD&D.  They were rather railroady but of the few dungeon modules I've bought I like them the best.  Yes, it's partly because I'm really into ancient Egypt.  I ran these for my group in college and they were a lot of fun.  Because I mostly play Pathfinder nowadays I'm thinking of working up a campaign in the not-Egypt land of Osirion in Pathfinder's Golarion game world.  These modules would work perfectly there.