This is a top quality site www.videodetective.com/movies/
You can watch the latest Trailers almost continuously,or select an old one, and it continues with the latest film trailers. The database has a lot of popular titles (No idea how big?)
Need Media Player to view it and it does support dial-up (Though on BB it's 10/10)
Sound/visual quality is excellent
Best thing it is free! There are some 30 second Ads between clips, but they are high quality exTV ads

Yeah, it's okay. It's helped me many a time for trailers. All the trailer sites I've been too have been free though. And I don't notice much difference in quality.

* Comes out of hiding for a moment *

Of the trailer sites I've visited, I generally prefer the collection maintained by Apple. The clips are of course, encoded for use with Quicktime, some are even available in HD-1040p resolution.