I've created a BBcode for GameTrailers.com video embeds now too. Seems to work OK for the most part but I've noticed slightly peculiar behavior with some videos that I haven't been able to figure out the cause for yet. Like with the [youtube] tag you can specify the video to embed either by putting a full GT video URL within the tag, or just the video ID, whichever you prefer.
For example, either of these produce the same result:
If anyone has an idea of why some videos end up bigger than the flash box they're played in let me know.
(Also disallowed the use of [youtube] and [gametrailers] tags in member signatures. Sorry to ruin people's fun but it does add significant amounts of bloat to have videos embedded at the end of every post you make.