If you're mailing something that's boxed and not flattening the box out and putting it between 2 cardboard pieces before mailing you're doing it wrong IMO.
I personally use various methods for mailing items. As for games, if they are cheapies like $2-$8 PS2, Xbox or Gamecube games - I put a piece of cardboard on the front and back and send them in thicker padded mailers. If they are a game that comes in a hard plastic case like PS1, Sega CD, Dreamcast, etc. - I package them in a box large enough that even if the post office tries to piledrive it, the game should survive intact. Games in cardboard boxes, I take extra precautions. I wrap them in bubble wrap, place them inside a walmart back and wrap that around them. I try to recycle, so I use whatever supplies I have on hand including peanuts, wadded up newspaper, etc.
The main goal is to protect the item(s), and that the more fragile the item - the more protection it needs. I also
avoid tight packing. You can wrap bubble wrap as tight as you want around a jewel case and put it in a box just a hair bigger. It still has a very good chance of getting smashed. For these types of items, I try to "suspend" them somewhere in the middle of the box, furthest away from the sides and corners.