As good as Portal 2 will be I don't see Valve releasing the game on it's own as a stand alone product like L4D or L4D2 , so is it possible that it could ship next  year contained in a "Orange Box" type bundle with Half Life Episode 3 and something else?

No. It's stand alone as detailed in a video interview.

I don't see why it wouldn't be standalone considering the single-player campaign is meant to be twice as long as the first, and then there's a whole separate co-op campaign on top of that.  However it's released I definitely need a copy though, so if Valve want to throw some other stuff in for free I won't complain!

Yes Standalone. Why would they loose money on this gem?

They said it was standalone but I think it might be difficult for Valve to do another Orange Box even if they wanted to. Two of the games in the original The Orange Box were old Valve classics that had died down (Half-Life 2 and Half-Life 2: Episode One) and Valve were aiming to revive and one game (Portal) was a very short game.

It will be bundled with Half-Life 2 Episode 3...is that the answer you were looking for?  ;-p

What else could they bundle it with that wasn't in the Orange Box? I wouldn't hold your breath for Half Life 3: Episode 3 :P

They said during E3 that Portal 2 will be a standalone game, but that doesn't mean they won't surprise us with a demo for HL3 or something (maybe the console version will come with their free PC "Alien Swarm" game), though I'm confident it will just be Portal 2.

Portal was always a gimmick...I'm not too sure if it's going to work as a standalone game.
 
Prediction - Good game but will bomb regardless without promise of much desired Half Life episode.

Hopefully it's standalone. Want more portal. 

might be included in one in the future, but right now its a stand alone game