Here's a useful one which hardly anyone knows: [noparse]. What it does is tell the vBulletin software to ignore any tags between [noparse] and [/noparse].
For instance, you know how you get the emoticon with sunglasses (8))when you have a numeral 8 at the end of a parenthetical statement? Well, if you put [noparse] in front of it, it won't do that. Example:
"(I haven't voted since 1968)"
"(I haven't voted since 1968)"
Here's the text for the second version:
[noparse]"(I haven't voted since 1968)"[/noparse]
Obviously, it's also good for demonstrating how to use tags, which is its original purpose.