As in, games that make use of procedurally generated levels to create a long life for the game without having to spend months on manual design work. In the indie game space, procedural generation is generally a popular design choice because of the replayability factor that it brings.
Anyway, what is on your list of the most well-made and varied games out there that rely on the endless procedural generation mechanism (along with those that have the best algorithms).
I just came across a video of a new game for iOS that come from developers who really know how to work procedural generation code and give an illusion of tremendous variety, called 1-bit ninja remix.
Not only do the levels look well crafted with the rather large number of procedurally generated set-pieces, it also intelligently increases the difficulty of level traversal the further you get. This actually looks like one of the few mobile endless games that would not get stale after a bunch of tries (as there are many on Android that only use a rather basic system for this type of thing).
What is on your list in terms of games with endless and/or unlimited levels thanks to procedural generation?