I liked that Blizzard went on a little bit of a creative angle with the Witch Doctor and I suspect they will do the same with the second class you refer to.  I wouldn't be surprised to see more than 2 more classes through really.

Who knows?  Wait and see.

One will be a ranged/druidic/assassin type character I think.ie. just a mix of those three classes to create the game's ranged class.eg. a ranger with a pet,bow(gun maybe) and cloak/shadow skills.

Second character will be a holy (paladin esque) class.Maybe predominantly melee with both dark and light forces , sort of like the Paladin in the Median mod.

The Range non caster class will probably happen. I want a morphing class like druid. That was pretty awesome! . Hmmmm Archiveist needs to be in that game... Quest bolt was so funny!

I can't back this up with a source, but I believe Blizzard has said there will be no Paladin in Diablo III, which bums me out and piques my interest at the same time; it'll be interesting to see what they replace them with.

My Guesses: Another Magic Dude
                         Paladin equivalent.
                         Amazon/Rouge Equivalent
                         Weird, Unorthodox class that we never see coming (Like the Archivist from the April Fools joke)
                       

Paladin, the others are all Brutes, there's no light, that and the fact he's super popular on D2.

However I'm disappointed to see teleport is still in the game, I hope it's just for evasion.

Does it really matter? You know your going to buy it, I know I am. ;-D  

As far as I know, 3 classes have officially been announced thus far.
And they are...
Witch Doctor (Necromancer replacement)
Barbarian
Wizard

If Diablo 3 follows the initial pattern of the 2nd game, that leaves 2 more classes available for launch. With 2 casters and one heavy melee class, I think it's safe to say that an amazon (ranged/melee non-caster) class is a safe bet, perhaps under a different name. That leaves room for one more, and probably is the more difficult of the 2 guesses. The other remaining classes (including the Lord of Destrucion Expansion) consisted of the Paladin, Druid, and Assasian. (All are essentially hybrids offering melee or caster/ options) Of these three, I'd prefer the paladin to return, but would probably be more interested if they ventured somewhere with a new class altogether...
Being able to play as an Archangel or something? (Out there I know, but shaking things up a bit would be nice, I think they made the right step with the druid class in LoD)

I don't know about all of you, but I would have preferred the older necromancer cosmetic over the new witch doctor...  I'll have to wait and see though! :)