This is the useful free software made available by Literate Software Systems that allows you to play many crosswords online or from your hard drive.

This is software (version 8 ranging from $49 to $169 as of September 2011) you should consider if you want to create crosswords.

Another professional-strength crossword creator, this program is similar to Crossword Compiler and as of July 2011 version 7 costs $59.95.

Barry Haldiman's superb Web site for seeing New York Times crosswords, and a lot more.

This already-historic site, by Jim Horne and now Jeff Chen, shows every NYT crossword and its answers in an extremely handy way, and it's reliable and inexplicably, almost magically, up to date.

But there's so much more.  If you are a constructor you already know about this resource.  If you are a fan of NYT crosswords you will be astonished at how much interesting statistical information Jim and Jeff have collected and have updated every day since November 21, 1993.

Much good information about crosswords, not just the annual tournament hosted by Will Shortz.

A forum for crossword puzzle constructors, this is a bunch of clever people talking about how to create and market crosswords.    Subscribing is free, and you can get a daily e-mail digest of posts.

This is the only mailing list I subscribe to, and I've read every post since I joined in January of 1999.  I've even contributed a few.

Pages from The New York Times Web site about their crosswords (duh) and other games, including forums.

Yet another forum for crossword constructors, this one restricts its membership to people who've passed a rigorous series of actual blood tests and DNA screenings to weed out the genetically nugatory.

BarnesNoble

Amazon.com

I list these links because the introduction of this book, edited by Will Shortz, is based in large part on a very small part of the very essay on crossword puzzles you're reading now.  Also, the cover apparently underwent an update from April 2002 to July.

The full title is The New York Times Monday Through Friday Easy to Tough Crossword Puzzles.

Amazon.com

BarnesNoble

I list these links because snippets of the very crossword essay you're reading now are quoted on a few pages of this otherwise commendable book (Oct 2001) by Coral Amende.

The full title is The Crossword Obsession: The History and Lore of the World's Most Popular Pastime.

Daily commentary on the good crosswords (including New York Times, Los Angeles Times, The Onion, Washington Post/CrosSynergy, Wall Street Journal, and more)

The puzzles are later explained and analyzed, and some of them are extraordinary.