Depends on the type of game. A high end RTS has about 500-1000 polys on a model, to make up for the fact that there will be a lot models drawn at once. An FPS on the other hand can range from 3000-10000 polies as there are fewer models being drawn at once. And you can get a lot of detail in 3000 polys. A really good model is a model that looks like it takes 20000 polys but only has around 3000. A racing game can have 20000 polys on each car.

It also depends on the system. These are all PC specs. I'm not even going to touch PS3, except to say that the new Splinter Cell was so damn good, I thought that it was a movie for the first half of the commercial.