Nethack is the only RL I play, just for fun not seriously. Just before the Quest NH becomes too hard for me. I wish Dev Team would release new version. You can always hope:)
We can place our bets in "What will come first, Duke Nukem Forever or Nethack 4.0.0?"
Anyway, my favourite roguelikes must be Angband (for its simplicity), ADoM (it brings good memories, it was my first RL), DoomRL (it is way too cool, but I cannot play it on 64-bit linux
), and maybe Crawl (since I've spent may hours in it too).
Incursion is looking really neat, too, I guess it will become a new favourite over time.
Truth is I am not playing roguelikes much nowadays. The university is really killing my free time.