Here is a downloadable game you can play just vist Pool 3D Training Edition 1.514. It is a billiard simulation game. I try it and it's a great game for me.

Although they are not free, my two favorites right now are Plants Vs. Zombies.  It's very addictive.  The developer was playing Grid Defense when he got the idea for the game.  If you have never played Grid Defense I highly recommend it.  They are both tower defence games.  Grid Defense is only $10 and well worth it.