Vocabulary Learning Fun is a free website that shares technology with SpellingCity.comThey recently added five educational word games that are worth bookmarking for regular use with your students:
Slang - a game that teaches common idiomatic English expressions
SAT Words - a vocabulary word game teaching a 1000 words commonly found on the SATs
Eight Letters in Search of A word - This is fun and educational to play in groups or alone.
MatchIt - This implementation allows you work your way systematically through the entire dictionary. It helps build grammar skills since there are various forms of the same word.
Letter Blocks - A great implementation of the word game where you form words from adjacent letters under time pressure to advance through levels.