DVD Studio Pro, unfortunately it is only available in Final Cut Studio 2. $1299. If you don't need the full suite it is kind of a high price to pay. (If you have any version of FCP you get an upgrade for $699)
But even if you don't want to use FCP the other programs are good to have
SoundTrack Pro and Motion are great for what they do.
Then there is now Encode for the Mac by Adobe. I have never used it or played with it, I'm just throwing it out there.