Several free puzzles are available on the MathsGoodies site.
A variation on crosswords are Crossums where all the clues are sums. You could print pdfs from this collection on the Teacher Resources on Line site developed by Frank Tapson.
Make your own crosswords with excellent free software – Eclipse. The grid shown in the image above was generated by the Eclipse program. Click on the image to download the crossword and solutions as a pdf. The program is very straightforward to use and includes a clear tutorial section. See these posts on reference resources for inspiration for crossword clues. Transum created this interactive crossword with the software from Eclipse.