I think an ejection should be done in a manner that is professional...does not make you (the umpire) the center of attention...but does allow everyone to know that somebody has been ejected. This is a mechanic that needs to be seen because it is letting everyone know that you are in charge of the game AND that you are getting control of the game back from somone who is attempting to rest that control away from you.
I use virtually the same mechanic as the umpire in this Youtube video did:
http://www.youtube.com/watch?v=AsEh_eFKz2U
When viewing this video, however, please note that after the ejection (when the ejected pitching coach goes ballistic) it appears that the umpire starts yelling right back at the coach and they go at it face-to-face. I absolutely am NOT suggesting that you do that. I am suggesting however, that the umpire's initial ejection mechanic is one you can copy. I use it on the high school and college levels.
As for what I say: while giving the mechanic I've been to known to say, "good-bye" or "that's it, you're done". Usually, I like "good-bye"...they all know what it means.