Cryptograms
All-Star Puzzles' Cryptograms, American Cryptogram Association: Crypto Drop Box, Between Waters, Copycreate.com Cryptoquote/Cryptogram, CRpuzzles, Cryptagram, CryptaGram, Cryptic Quoter, Crypto Challenge, Crypto Daily
Mathematical
CellFighter, CrocoPuzzle, Dave's Logic Puzzles, IBM Research: Ponder This, Jim Loy's Puzzle Page, Leisure Ideas: Puzzles, Mathematical Jigsaw Puzzles, Monty Hall Game, Perplexus, Quick Logic Puzzles
Nonograms
Conceptis Puzzles, Elite Japan Crossword, Paint by Numbers, Solving Paint-by-Numbers Puzzles with Integer Prog, The Jcwd
Optical Illusions
Akiyoshi's illusion pages, All Optical Illusions, Amazing Eyetricks, Amos Storkey - Visual Illusion of the Month, Cool Optical Illusions, Cut the knot: Visual Illusions, Eye Magic: Optical Illusions, Eyetricks.com, Fun puzzles, IllusionWorks
Riddles
A Collection of Quant Riddles, Able2Know, Amusements in Mathematics, Brain Teasers, Brainbusters, Daily Outrageous Rebus Riddle Contest, DiMensIoNS, Fleabusters' Kids Fun Page, Harder Riddles, HumorShack
A Game A Day
A puzzle site featuring a new puzzle format each weekday for each month. Puzzles are fun, educational, entertaining and are also printable.
Able2Know
Message board of user submited riddles and brain teasers.
Abnorm's Conundrums
Easy, medium and difficult brain teasers without answers.
All-Star Puzzles: Logic Problems
Collection of logic problems to solve. Printable.
Alphabet Cartoon Puzzles
Letters of the alphabet are used as structural components for drawings of figures and faces. Spelling tips lead to the solution of the puzzles.
Archimedes' Laboratory
Recreational mathematics including puzzles to make and solve, tessellations, geometric puzzles, optical illusions, and curiosities.
Bill's Brain Teasers
A collection of visual and linguistic riddles.
Brain Juice
An assortment of entertaining logic puzzles with solutions and indicated levels of difficulties.
Brain Teaser World
Offers riddles, puzzles, optical illusions, and magic tricks.
Brain Teasers
Brain teasers, riddles, logic puzzles and problems, paradoxes, optical illusions, IQ tests and logical games.
BrainBashers
Brain teasers, puzzles, riddles, games and optical illusions.
Braingle - Brain Teasers & Riddles
Contains a huge collection of user submitted and rated brain teasers and riddles. It also has a lively message board and some unique multiplayer games.
ButlerWeb
A page of about 30 brain teasers. Answers are hidden in drop down screens.
Chronigma
Weekly competition to solve original puzzles, riddles, and brain teasers in the least amount of time.
Curiouser.co.uk
Paradoxes, puzzles, games, optical illusions, poetry, curious facts, and quotations.
Eluzions
Featuring all sorts of games, optical illusions, puzzles, trivia, mazes, and magic tricks. Suitable for all ages.
Eye-Pleasing, Mind-Teasing 3-D Conundrums
Scans from a book of puzzles, includes English translations.
Gamekeeper's MegaQuiz
Quiz, hangman, and images. Quizzes are downloadable and require Microsoft Excel on PC.
Gray Watson's Brain Teasers and Riddles
A collection of brain teasers and riddles with a guess button.
Had To Play On
A community based site with competitions, challenges, awards, a help centre, forums and games.
iRIDDLER
Challenge your mind with free online riddles/puzzles, logic games, brain teasers and view optical illusions.
Just Riddles and More
Riddles, illusions, puzzles, and brain teasers.
Logic Puzzles Escapades
Logic puzzles with a satirical New Zealand tone.
National Puzzlers' League
Crosswords & other word puzzles and games, samples; monthly puzzle magazine; 800,000 word searchable list.
Nonogram Solver
Information about Nonogram logic puzzles and how to solve them, plus examples of two on-line solvers, software, and links.
Peculiar
Brain teasers, problems, mathematical mind mazes, questions and optical illusions.
PedagoNet Brainers
Over 60 brain teasers to enhance your mind
Planetarium
An on-line puzzle story in twelve weekly installments.
Professor Tangent
Have fun with games, puzzles, brainteasers and humor as you learn about logic and analysis.
Purple Hunt
A fun site for puzzles, free games, treasure hunts, cryptograms and intrigues. Prizes for winners.
Puzzle Contest Center
Riddles, brainteasers, cryptograms, anagrams, and logic puzzles. Compete in eight new contests monthly.
Puzzles on Seniority
Riddles, mind benders and puzzles for seniors (aged 50 or above).
Puzzles Without Rules
Free, updated, original abstract puzzles for advanced puzzle-solvesr. Includes current unsolved puzzle and archive with hints and solutions.
Rec.puzzles Archive
An archive of many popular puzzles from the rec.puzzles newsgroup.
Roh'El's Riddles
Offers brainteasers rated by difficulty and category.
Say What You See!
Collection of visual brain teasers which can be solved by saying what you see.
Shashi's Homepage
Collection of puzzles, riddles and brain teasers.
Ten Teasers
Some of these brain-teasers need some thinking, others need no thinking at all.
The Amazing Art Site
Huge collection of optical illusions, hidden imagery, ambiguous art and upside downs.
The Game: What is The Meaning of Life?
Game with clues to answer the question.
The Grey Labyrinth
A beautifully illustrated collection of puzzles, riddles, and paradoxes. Features a changing "unsolved puzzle" plus three years worth of previous puzzles.
The Logic Zone
Collection of problems with answers, logic puzzles and cryptograms.
The Puzzle Meisters
Features puzzles and mysterious enigmas along with a few trivia questions here and there.
The Stone
an online mystery game. Hours of clever puzzles and riddles. Puzzles challenge the mind of serious and amateur players worldwide.
The Ultimate Thinking Puzzler
Discover who killed Ronald Opus in this contorted thinking puzzle.
Toon and a Mindtrap
Answer the daily brain teaser emails to become Mindtrapper of the month.
Unitix Entertainment
Online games, puzzles and other interactive brainteasers. Fun for all ages.
Word Juxtapoz
Word puzzles, riddles, rebuses, brain teasers, mazes, cliparts and pictures.
Wordles!
Get free cryptograms, create your own, and look up crossword puzzle words.
Zuzzle Puzzles
Collection of puzzles including riddles, logic puzzles and sequential puzzles.