Anyone know a site where I can find a complete list of FIA, SCCA, etc. classes and rule changes?

Along with, preferably, the cars that raced in each class. I haven't had much luck finding such a thing.

 

I suggest Google

 

I've been trying that, see OP.

 

https://en.wikipedia.org/wiki/Template:Class_of_Auto_racing
https://en.wikipedia.org/wiki/Template:FIA_classes
https://en.wikipedia.org/wiki/Category:Racing_car_classes This one have some of the same links from above.
http://www.scca.com/pages/car-classifications-and-groups I can't blame you took me a while to find this.
http://www.rally-maps.com/home WRC/rally stages

What do you need this information for? Just wondering.

 

Totally of topic but where do you get that signature picture of your focus?

 

You can find them here, you are going to need an account. http://www.pixelcarart.com/index.php?act=idx
I then cropped the picture and put back in the credits and an outline.