Isn't it strange that I was just about to post about BBComposer !!
Now that BBCode extension seems to have died (it isn't compatible, at least by default, with recent FF updates and the website has disappeared) I was looking for an alternative.
I just discovered BBComposer and it seems quite neat to me, espeically for people who can't be bothered to remember all those BB codes.
As well as the links AbteriX provided it has its own website
You still can't easily add square brackets inline without having to use a code block though.
I'm pretty sure there is a BB code for cancelling formatting temporarily - but I can't remember what it is!
Edit: OK I found it .. the code required for no formatting of any kind (and without putting stuff in boxes etc) is NOBBC
eg. [B]test[/B] is generated by the fragment
Mouser - how about a NOBBC button in the editor near the Code button ?
A useful source of further BBCode tags is at SMF's website