I imagine many of you have heard of "Easter Eggs", but if not, they are fun little extra hidden bonuses on your DVDs. Sometimes they are pointless, other times they are amusing extras, but they are almost always cool on some level.
Below is my favorite site for finding them. It may not be an exhaustive list, but I've found it to have many listed that are out there. Just use the link and search for some of the titles in your library.