I've started adding crossbin puzzles to cse4k12.org. Crossbin puzzles are similar to crossword puzzles except that the clues are hexadecimal numbers and the answers are binary numbers.
When the puzzle is complete, the grid is filled with '0's and '1's. Then all the '1's can be filled in with black (and, optionally, '0's erased to white) to create a simple black and white image.
These are useful as a simple exercise in a computer science class after the students have been introduced to binary and hexadecimal numbers (and how to convert between them).
Basic instructions and a simple example are given at cse4k12.org: