I was curious what file formats my Samsung D550 series TV would play. (PS51D550 since you ask, and its great). Tucked away on this page is a table, which I've reproduced here.
Huge number of formats. The reason I did this was to check and confirm that it would not play .m4v files that iTunes likes, and can be produced by HandBrake. HandBrake can do .mp4 as well of course, though you lose chapter information which can be useful.
If you do have files with .m4v extension, you can change the suffix to .mp4 and they will play OK from USB.