I didn't think that much can be done with the premise of "Pong", just some slight refinements here and there via a few games. Boy, was I proven wrong! "Plasma Pong" was an indie game, done by one person, that was released a few years ago (2007, I believe). It is free to download for PC.
Plasma Pong is basically Pong, with paddles, ball, and black screen. But there is one key factor that influences the gameplay significantly, and makes it into almost a completely different game. The field between your paddle and your opponent's is a field of plasma, that can be molded and manipulated via your paddle. Your paddle (and your opponent's) can be used to shoot plasma, which influences the direction of the ball. This causes the ball to go into wildly divergent patterns, and there are often times when the ball will fly into the plasma made by your opponent, causing the ball you just shot to come flying right back at you. You can also use the plasma to suck the ball into your paddle and release a shockwave that will send the ball speeding towards your opponent.
The game is not a best of 10 or 11 set as in regular Pong, but every time you get the ball past your opponent, you advance to the next level, where the plasma becomes even more plentiful on the field and it becomes harder to determine the path of the ball. You get 10 lives, and lose one when a ball slips by you.
The graphics are pretty amazing. The plasma that is shot quickly turns the black screen into a cavalcade of vibrant colors. Potheads could really appreciate this game. During gameplay, pressing 1-9 can alter various graphical elements of the game, including 3D, plasma shading and temperature, creating even more graphic variations. The music is an orchestral/dance hybrid of some kind, and you can hear its tempo speed up every time you go to the next level.
There is also another mode called Sandbox that lets you tamper with the graphical effects of the game without having to play it. This is good if you just want to sit back and treat yourself to a light show.
The only issue that I have with the game is that I wish it had gamepad support. It only supports the mouse, and I found that using it tightened the control up more than it should have been. Maybe a trackball mouse would work better with this game. Other than that, I have to wholeheartedly recommend it, especially since it's free to download.
(Note: The developer, Stephen Taylor, closed the website promoting the game [www.plasmapong.com} due to its infringing on the Pong trademark. There is a note on the website promising an update of the game, along with another new game from Mr. Taylor, but neither seems to have materialized; the notice was published in 2008. It's a shame, because it is a very good game.)