Boggle - Classic word game. Search for quick words to make.
Theme Poems - Poem-making app that lets you send poems to your teacher or friends. I really like this one!
Jumble - Word scramble. Made for adults so it may be difficult.
Word Confusion - Choose the correct word to go in the sentence.
Grammar Gorillas - Check your knowledge of adverbs, nouns, prepositions, etc.
Channel 4 Learning - Awesome site that explains poetry and rap. It has a few word games too.