Dicewars for sure.
Try this one from them as well:
http://www.gamedesign.jp/flash/crossword/crossword.html
Stupid hardest level took me long enough that I printed it and put it on my wall at work.
EDIT: Hm, they maybe changed it, before the hardest level had no hints at all!
EDIT2: They did change it! Bah! Before it had an open crossword with no letter hints, and all 26 letters to work with. They made it easier