Crossword Grids (Jean-Charles Meyrignac)Discuss about this problem
Using the ENABLE2K word list (http://personal.riverusers.com/~thegrendel/software.html), put letters A..Z plus blanks into a blanks-surrounded 15*15 square grid such that all formed words between any two blanks horizontally or vertically are in the given wordlist.
Maximize the number of A's.
Each word may only occur at most once.
Do the same for all the other letters B to Z.
http://www.maa.org/editorial/mathgames/mathgames_05_10_04.html

NEW !

An easier variation is called Zwyggle.
The aim of the game is to submit a grid of N*N letters, so that they form the longest possible words horizontally and vertically, like in Czech crosswords.

Here is an explication in french:
http://zwyggle.free.fr/2regle.htm

Here is an automated translation into english:
http://translate.google.com/translate?u=http%3A%2F%2Fzwyggle.free.fr%2F2regle.htm&langpair=fr%7Cen&hl=en&ie=UTF8

It's very similar to Czech crosswords: http://www.lusk.cz/puzzle.php?lang=en&id=2599

For each letter A...Z, submit a 15x15 crossword grid with the most occurrence of this letter.