Derek Yu has released a new game called "Spelunky". It's still in the beta stage, but perfectly playable and he's offered a download on his website.
According to his description:
"Spelunky is my latest game project, a hybrid of two genres of games that I enjoy - the roguelike and the platformer. The idea partly came from playing around with both genres separately. It was like I baked two different kinds of pies and then I stepped back and looked at them and finally just mashed them both together. Does it taste good? I leave that to the reader to decide."
Check it out. Derek Yu's Website