Crosswordsite - Both American and British English styles graded from easy to hard for solving online or on paper.
Fernsmacker's PuzzlePick - Features three different puzzles: a weekly cryptic crossword, a monthly double acrostic and a twice weekly trivia puzzle. Subscription needed.
Guardian Unlimited Crosswords - Paid crossword subscription site with puzzles that can be solved online or printed out.
The New York Times Crosswords & Games - The daily crossword puzzle with four ways to play, plus free classic crosswords and trivia quizzes. Subscription required.
Times Online - Offers paid subscription to weekly and monthly puzzles from The Times and The Sunday Times.
The World's First Crossword - Read about and solve crossword by Arthur Wynne, first published in the New York World in 1913.
XWord - Crossword Compilers - A collection of various styles of puzzles by Anina Roux and her team, compiled for magazines and newspapers in South Africa.
Xwords.co.uk - Play online or print and solve. Also offers creation tool. Registration is free.
Yahoo! Games: Crossword - New puzzles daily, archived for two weeks. Free registration required.
csmonitor.com - Play on words - Discussion about the documentary movie 'Wordplay' which shows how people from different walks of life relate to crossword puzzles.