I hope to show you a range of what is available. Although there are quite a few jQuery games out there, I chose these for their playability and completeness. You can tell these guys put in a decent effort to make a quality product.
I'd like to start with the jQuery pong clone. Why play against your friends when you can play against your browser! This game has a whole bunch of options that you can set yourself if you decide to download it for yourself including ball speed, score to play to and paddle sizes. Click on the image to follow the link.
The next game is extremely addictive, but based on a simple idea. In jCharacterfall, water drips from the ceiling and you stop them from hitting the ground by pressing the matching letter. As the game goes on the drops fall faster and faster. Hours of fun!
Next up is a sudoku game. This is a nice clean implementation and is a real challenge to get your name up in the highscores (not like all the other hacked high-score lists!). Only thing I think is missing is the ability to pencil in smaller guesses.
Sticking with the retro theme is an old fashioned snake clone. You know the score, snake goes round, eats stuff, crashes into walls.
The next one is really special and a lot of effort has gone in to building it. Jon Raasch has built a clone of the old NES game T&C Surf Designs. It looks and handles like the classic Nintendo game and the sprites look great.
If you have any more suggestions for great jQuery games leave a comment.
Have fun and enjoy!