Pretty much all of the game trailers are HD on the marketplace, dunno about the movies never really looked.
PSN does have some HD movies trailers but it's been pretty much the same 30 or so trailers forever but they are good so if u have a ps3 check em out.
Or go here and download some and whack em a dvd to play in 360 or ps3 etc, some are spectacular quality and some the best HD ive seen.
Avoid the first section, just snippets from start of dvds/titles etc.
Sorry that was my mistake in my other post, Assumed i had played them in both 360 and ps3 but i hadnt i'd just used my PS3. Have a DVD with over 4gb of them on and assumed id tried it on 360 but hadnt.
Without converting somehow they not gonna work then sorry, i did just try a converter and it ended up a HD MP4 file and didn't look very good compared with the original top notch quality files.
Got a ps3? lol
Some of them clips are staggering quality really are.