EDIT: Sorry about the double post guys...
Okay, so there seems to be a lot of debate about the final roster size. Let's look at this in a logical fashion, shall we?
Now, let's take the existing roster of 26. Without debating who it might be, let's say at maximum, they take out 8 of the Melee roster (and I do stress, 'at maximum'). It will probably be less, but I'm just trying to get a ball park minimum for the new game here. Also, this remaining 18 includes redone characters, such as a new moveset for Ganondorf or a Wind Waker variation for Young Link.
Now, we know of four definite newcomers - Meta Knight, Pit, Wario and Snake - so that bumps us up to at least 22.
Of course, in Melee, we were treated to 14 new characters. I would expect that Sakurai would be mindful to match this at the very least, which means an extra 10 characters on top of the 22 so far, leaving us with an educated ballpark minimum of 32.
Of course, I know a lot of people have made an educated guess, but god, have I seen some stupid **** said on this forum regarding the roster size...