Great question. Tal was very original in his sacrificial play. Petrosian used the exchange sacrifice a lot, more than other champions. Supposedly Gurgenidze was very unconventional in his openings. Back to Petrosian - he used to make really "strange" moves, putting the pieces on the edge of the board, for example. Steinitz moved the King a lot. This just off the top of my head, there's bound to be more.
Most original player ever

Ljubojevic. Really crappy openings, never studied theory much. Pulled off some great upsets in the '70s. Tony Miles. Used the obscure Owen's Defence a lot (1.e4 b6!?). Played 1...a6?! against Karpov and won.
http://www.chessgames.com/player/preston_ware.html
Preston Ware Played in a lot of tournaments but not with good results due to his unconvential Openings.1.A4 2.A5 . He attended the 5th American Chess Congress.Also known to break Stientz winning streak.

I would probably not vote Shirov, but at least his name should be mentioned as well in this list.
Originality in my view is generally about playing according to your own thoughts, instead of what you've learnt by other peoples thinking. In modern chess (at top level) being truly original seems less and less possible.
The most original I can think of is Nimzowitsch, with his bright views (correct me if I'm wrong, but relatively modern views) on the game as he described in "my system"

No such thing.
Stop asking silly questions that have no real answer, can in no way enlighten, and only serve to cause dissention and create arguments.
I disagree.I think it is a very interesting question,thank you.
No such thing.
Stop asking silly questions that have no real answer, can in no way enlighten, and only serve to cause dissention and create arguments.
I disagree.I think it is a very interesting question,thank you.
That's because you young and foolish and ignorant.
That's because you are young and foolish and ignorant. *
No such thing.
Stop asking silly questions that have no real answer, can in no way enlighten, and only serve to cause dissention and create arguments.
I disagree.I think it is a very interesting question,thank you.
That's because you young and foolish and ignorant.
That's because you are young and foolish and ignorant. *
That's because you are young, foolish and ignorant. *
Im still holding onto my vote with Preston Ware the dude was fearless with his opening choice.Even without his Opening he was a tough boulder to move.

Breaking the rules for the moment here, to nominate a chess problemist.
The other day I was paging through the huge Laszlo Polgar book, 5334 Problems, Combinations and Games. Many of you will easily recognize this "brick", which is essentially thousands of diagrams to be solved. I chanced to have looked at this white to play and mate in two problem, number 745:
Looks like a piece of cake; the black king is surrounded, any move should do. A minute passed, nothing. Couple of minutes, and there is no way that black can be mated in two - there is always a way out, it seems. Frustrated, I looked up the answer.
There is a mate in two here, it turns out, and as soon as I saw it I realized that this is the famous Sam Loyd problem rotated around the vertical axis ! So the kingside becomes the queenside...
Coming to conclusion, I nominate Sam Loyd as one of the most original problem composers ever.
Who was/is the most original player ever?