If you're anything like me, you've played so much Spelunky that you can close your eyes and generate new levels for Derek Yu's roguelike platformer inside your own head. Here, look, I'm doing it now - bet on what's going to kill me...
It was a frog. Sigh.
For a more technical understanding of Spelunky's procedural level generation, take a look at Darius Kazemi's browser-based Spelunky level generator and associated guide.
Part one details how Spelunky generates rooms while guaranteeing there's always a route to the exit, while part two goes into more detail about the positioning of probabilistic and obstacle blocks. It's not the kind of information that's likely to make you any better at overcoming the gamut of obstacles the level generation spits up in a typical life, but it's a neat glimpse of how those challenges are created, and sure to be useful to anyone thinking of making a similar system in their own game.
I'm just new enough to this whole internet-writing thing that this feels to me like a magazine boxout come to life. I look forward to reading the real-time letters pages that will appear under this post later.