Since Googling is the most common and easiest way to search for anything this is merely a collection of some of the more usefull sites I have found. Let's say I want to find a song that is in a commercial. I can google "search for songs from commercials" and find a list of sites that do this. But that may be more typing than you want to do. Maybe it would be faster to just do a few mouse clicks and go to a site listed here. Espescially if you are familiar with this site you can just click click click and boom you're there. This is how it is supposed to work anyway. We'll see.