[Elladan and Elrohir]

Wow, I can just picture him doing that. Scary.

Actually, although it does say that in Unfinished Tales, I don't think Tolkien was set on there being more than five wizards. He gives an account of how the Valar came to send the Istari to Middle-earth, and in that account it is clear that there are five and only five. For myself, I think it makes a lot more sense for there to have only been five (after all, their purpose was to battle Sauron, and only one out of the five we know of did that successfully).