I have just discovered a not-quite-accepted punctuation mark I wish I had always known about: the interrobang. It's a combination of an exclamation point and a question mark. As someone who has always resisted using more than one punctuation mark at the end of a sentence, this is a godsend.
So hey, publishers and software developers: let's get working on spreading the interrobang! I would like to be able to use it while posting a blog entry instead of pointing people to the Wikipedia page, which has some lovely pictures of it in different fonts.