Many studios that produce DVDs have favorite places to provide access to hidden features. As with other hidden features these can range from the mundane to the very interesting. If you can add to this list please let me know by means of the FeedBack page.
In many Universal releases the complete sound track of the movie will play during the Main Menu. In movies such as Apollo 13, this is an incredible find since the soundtrack is commonly in Dolby 5.1 which beats out the CD release by a long shot.
New Line Cinema
Look for the New Line Cinema logo on the Main Menu. Hit will usually provide the credits for the production of the DVD.