Nice collection of DD, THX, DTS logos in DVD's VOB format:
<a href="http://www.cinenow.com/fr/vobtrailer.php3" target="_blank">http://www.cinenow.com/fr/vobtrailer.php3</a>
(Files are very big and can be played with PowerDVD or WinDVD).

Also on roth.ru I discovered great collection of classic trailers (Forrest Gump, Rambo, Jaws, Star Trek etc.) in hi-q DivX format. Don't miss them.