Every morning I like to do the Codeword games on Brainbashers.com.
This morning, I found there are Physics crossword puzzles!!! I have done the first two so far (you can change puzzles in the bottom left hand corner of the screen). The first was a bit advanced for high school students, but the second one was much more appropriate. It might take some work to find the appropriate puzzle for a given class, but it’s comprehensive and covers roughly a whole year of Physics.
Along the same lines, there are website such as Crossword Puzzle Games where you can create your own crossword puzzle for free. This makes it easy to customize puzzles for use in your classroom!