I just got done doing some updates to a forum I admin, and I was browsing through/adding some BBCode tags that would be useful.
Some of them I was noticing would be EXTREMELY useful on this site.

The list I was looking through was ad-ons for SMF, but I'm sure there are similar ad-ons for vB.

Some of the tags I liked were:

[you]
This one isn't super useful, but pretty entertaining... when it parses out, [you] is replaced by the username of whoever is reading it.

so.... if you did something like:

Has anyone noticed how crazy [you] is?

And to anyone that looked at the post, they would think you were talking about them



[countdown]
ok, this one actually could be really useful for threads about events or even for people to put in their sig.

Basically you put a date/time in it, and it parses out to a countdown until that date/time, once the countdown reaches zero, it replaces it with whatever is in the tag

So, for example, this:

[countdown=1,1,2012,0,0] End of the world! [/countdown]

would parse out to:

4 months 18 days 7 hours 41 minutes remaining.

but then 1/1/2011 after 12:00 AM it would switch over to:

End of the world!


Like I said, this would be really sweet for shows/events/etc...




There's also some that are stuff like
[only_member]
[only_mod]
[only_admin]

Those hide the text inside from everyone except in the usergroup that is allowed to see it. (for example, only mods/admins could see something between only_mod tags)

This one could be useful for two reasons... Mods/Admins could make moderation notes right in the midst of a post, and also if someone wanted to make a remark specifically to a moderator in a thread, inside of a post, they could do so.
Also, with the only_member one, people could easily say stuff in a post that they're fine saying to another member, but don't want readily broadcasted for the whole world to hear.