So, sharing this bit of information, as I feel that it's not very clear and I only found out by accident.
Say you have a YouTube video, and you post the link into your comment. Now that's great and all, but you want it to show up as a video, not as a link. Well, after you past that link, press enter.
Yep, it really is that simple. It will pop the embeded video in there for you and tada. You can do the same with image links.
See ya'll in the Wasteland!
(Example and shameless plug):