Looking for a roguelike to play? Here's a short list of some of the more interesting roguelikes I've come across (descriptions taken from RogueBasin):
1) Ancient Domains of Mystery (http://www.adom.de/) (my personal favorite)
The game is set in the world of Ancardia, an original creation by Thomas Biskup. The objective is to find the source of chaos and disorder that is arising in the world, and stop it if you can. The game is much more plot driven than many other roguelike games, with many beings in the game assigning you quests, giving you advice and helping you on your way. There are a few compulsory quests, but the majority of quests and tasks in the game are optional. There are also multiple possible endings to the game.
2) NetHack (http://www.nethack.org/)
In NetHack, the most popular of Hacklike games, you must fight your way down through the Dungeons of Doom, and then the underworld (Gehennom), retrieve the Amulet of Yendor, fight your way back up to surface, and give the Amulet to your god.
3) Labyrinth of Reptoran (http://reptoran.roguelike.us/)
The Labyrinth of Reptoran is the first in a series of roguelikes planned by Jared Brayshaw. It is going to be a dungeonhack, with a large town on the surface and 100 levels of random dungeons underneath. This game is different from standard roguelikes mainly in how it approaches skills, magic, combat, and quests.
4) Crawl (http://www.dungeoncrawl.org/)
You choose a race and, based on race restrictions, a class, then dive 27 levels to retrieve the Orb of Zot before ascending back to the surface. On your descent you will need to make side trips to branch dungeons to acquire "runes", keys needed to enter the Realm of Zot.
5) Deep (http://www.deep.homepage.t-online.de/)
Deep is a graphical roguelike game written by the German developer Oliver Mecking. This roguelike is easy to access, due to only a small amount of hotkeys, graphics which speak for themselves and an easy, forgiving gameplay. You can also save whenever you want (for a little gold fee) or restart the dungeon with the same character and all his equipment. There is only a single dungeon, but its theme changes every 10 levels and there are lots of special rooms, boss enemies, unique items, secrets and npcs, all of which appear randomly (more or less).
6) Angband (http://rephial.org/)
Angband is a freeware roguelike based loosely on the works of J. R. R. Tolkien. It was created by Alex Cutler and Andy Astrand at Warwick University in 1990. It is named after the fortress of Morgoth in Tolkien's works, with "Angband" literally meaning "Iron Prison" (or "Hell of Iron"). The latest version is version 3.0.8, released July 8, 2007, which is available for a wide variety of platforms.
Of course, that's only an extremely small list compared to the hundreds of other roguelikes out there. Is your favorite roguelike not listed here? Post the name of it in the comments so we can all try it out!