I thought I read some where that CS5 comes with a lot of stock footage, effects like explosions, and different back grounds.
Ahh... no. There are some title templates, but I wouldn't call those stock footage. Not anything to get too excited about...
Can you point to where you read that?
PS comes with some "stock images," but PrPro never has.
In the past, PrE came with some sample footage, for learning and testing, but that was all.
One source of stock footage is Muvipix, and it is available for purchase, or free to subscribers. The list is stock footage, Menu Sets for PrElements, original music, and some more.
After Effects comes with some loopable backgrounds.