If you are looking for a simple ang free game to improve your vocabulary, then WordTwist U for iPad is worth a try. WordTwist U is a very easy game to play, very similar to Yahoo's Text Twist.
The object of the game is to make as many words with the six given letters. In order to proceed to the next level, the player must find the word r words that use up all the letters before time runs out. Once this word is found, the player can choose whether to proceed to the next level or continue finding other words until time runs out.