NetHack
Official site. News, guides, links, and both source and executables for several platforms.

NetHack Stuff
Dictionary, world map, and play statistics.

rec.games.roguelike.nethack Cretins Advisory
Dedicated to keeping the newsgroup clean of "spammers, d00dz and things like" that.

rec.games.roguelike.nethack FAQ
Frequently asked questions about the game, its Usenet newsgroup, and related topics.

Sascha's and Ralph's NetHack site
Includes spoilers, hints, utility programs, and a list of public NetHack servers

The NetHack Dungeon
Hall of fame, tips and tricks, spoilers, and other files for the 3.2 release.

The NetHack Home Page
Unofficial mirror site. Spoilers, source, executables, and utilities.

The NetHack Index
Annotated directory of spoilers, variants, patches, utilities, servers, reviews, and other useful information.

Yahoo! Groups - thenethacklair
Gameplay discussion group. Free membership required to participate.