In case anyone doesn't know this yet, when posting any of the following content types, all you need to do is paste in the direct URL to the file, and the forum will automatically embed it for you.
YouTube
Google Video
MySpace Video
GameTrailers
YouTu.be
Flickr Image Set
MP3
Flash Movie/Game
Vimeo
Soundcloud Audio File
If for some reason it does not embed the file automatically, you can always use the media bbcode tag like this:
[media]https://www.youtube.com/watch?v=MODNI9JReu4[/media]