Playing something like Scrabble or Bookworm Adventures? Stuck for what you can make from the random letters given to you? If you're playing at home, alone, no one will know if you cheat... just a little... and JeuDeMots from Neogie is the free tool that will help you do it.
JeuDeMots is extremely straightforward. Type in some letters and click "Search", and it will find words made from those letters, or starting with those letters, or rhyming with a word you typed, and so on. You can filter the resulting list by word length, or you can attempt to find a definition on Wikipedia (Oddly, not Wiktionary, which would be more useful in this case.)
That oddity points out, perhaps, why JeuDeMots is free--it's nifty but incomplete and buggy. JeuDeMots has no "smarts" about specific games, so it will produce many words which aren't legal in, say, Scrabble. The function for finding rhyming--sorry, "riming" words seems to rely on letter patterns, not sounds--thus, JeuDeMots tells you that "selfwilled" rhymes with "while". Although the version available here is the English language version, its mouse-over tooltips are in French, as is the error message I received when I tried to use the spellcheck function. Quel dommage.
As a freeware utility, JeuDeMots is worth it--barely. It may be very helpful if you're stuck in a "make a word" type game, but those who play Bookworm Adventures for blood will probably find it underwhelming.