Jeopardy Labs is a free and easy-to-use tool to create and run Jeopardy games.  Playing and scoring is easy to manage.  When you create a game you are asked to give it a password.  The game will be assigned a unique url (that you should bookmark/favorite) once it's created.  In order to play, just return to the url and enter in the password.   
Jeopardy Rocks is a free tool for creating and playing Jeopardy style games.  The games play smoothly, however you have to give points for the question prior to revealing the answer/question. 
Flip Quiz is a Jeopardy style game creation tool.  They offer a free version and a premium upgrade which gets you features such as the ability to add images to your questions.
E Quiz Show allows users to create and manage Jeopardy games.  It has a free and a paid version.  The free version allows for game play between two teams.