Mathematics for Computer Science
Links

Databases and Logic

• "Factasia" on logic with special section on elementary propositional logic and predicate logic
• Wikipedia's entry on naive set theory
• Microsoft Access Training Courses (by Microsoft)
• H2 Database Engine (supports all set operations)
• SQL Fundamentals by John Patrick (introductory book on SQL for Access and Oracle)
• Practical SQL Handbook by Bowman, Emerson, Darnovsky (book covers several SQL dialects)

Puzzles and Combinatorics

• Cornmaze in Illinois
• Mazes, including tilt mazes
• How Would You Move Mount Fuji, by William Poundstone; interesting book on puzzle interviews. A lot of the puzzles are online too.
• puzzles.com, tons of interesting puzzles of all types
• Sokoban, addictive game. Not the best version (that would probably be Sourceforge's Sokoban, but that requires installation).
• Tangram, another addictive game. Best played with real pieces.
• planar graph applets, play with straight-line drawings of graphs.
• Euler's theorem, a different take

Cryptography and Algebra

• The Code Book, Simon Singh, Anchor, 2000; Popular historical account of the history of cryptology, with a fair amount of technical detail. An excellent and instructive read.
• Elementary introduction to modular arithmetic
• Psychic webpage (how does it work?)