I was looking for some help playing the game WordBreaker on my iPhone and discovered that OS X's Dictionary program can help you find matching words given a set of letters. For example, enter ?oat, and Dictionary will give you a series of words like boat, coat, and goat. Very handy for crosswords, too.
[robg adds: In testing this, it seems you can use only one wildcard per word. Also, I was able to get slightly different results using different non-alpha characters. Using bea?, Dictionary returned eight matches, but bea! only returned seven. You can also use the wildcard within a word; b?ar shows both bear and boar. Based on how this works, I'm not sure if it's a bug or a feature -- Dictionary's Help says nothing about it at all.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070706090019787