6 links
Crossword Puzzles for ESL Students
iteslj.org
A selection of online crossword puzzles sorted by difficulty.
Mockok.com
mockok.com
A large collection of palindromes, focusing on palindromic single sentences (spelling the same forwards and backwards). Submissions welcome.
NOVA: Decoding Nazi Secrets
pbs.org
Crack the ciphers, send a coded message, and find out what goes on in the minds of code-breakers.