Quizlet: Login to Quizlet.com and embed any study set by clicking More on a set's page. Then click Embed. Choose the code for the set's Flashcards, Lean, Match, Spell, or Test modes.
Classtools.net: Classtools offers a variety of games and activities for students. Embed code is provided for many of them, including the Crossword Generator and PacMan. Note that some of the games on Classtools.net require Flash.