Randomly label each side of a number of home-made cubes (foam, styrofoam, sponges, wood, sugar, paper, etc.) with alphabet letters, or use Boggle cubes.
Toss all the cubes onto a table and give yourself a specific amount of time to find as many words as possible, using any of the letters facing upwards. A letter can only be used once in each word (unless more than one is thrown), but can be used in as many different words as you like.
This game can be played with others, either as partners where they work together to find words, or in competition, each person writing as many words as he can within the time limit.