I think its fame almost precedes it to a point, but Death Frost Doom is a really great module, and playing it with a group that doesn't know it is a really tense and rewarding experience.
In terms of more recent stuff, Gardens of Ynn is really great, as is almost all of the stuff by Hydra Cooperative.
While it isn't a module per say, Veins of the Earth is probably the best game book I've ever read. It's really incredible.