Thought it might be interesting to try to list every legal black reply against the Tarrasch. My database of recent TWIC's has got black trying no less than 14 moves

Completely respectable: c5, Nf6, dxe4, Be7, a6

Nearly respectable: Nc6, h6, b6

Sensible looking(but 'rare'): Bd7, Ne7 (Ne7 isn't that rare in fact), Nd7

Rather Dodgy looking: f5,g6

Bizzare looking: c6, Bb4, Nh6, Bd6

I think that covers all the games in my two databases That leaves the rest I suppose. I imagine larger databases have a few games with some of these.

Potentially 'playable' (for a pretty loose defintion of playable you'd think): Na6, a5, f6, Qd7 

Very likely bad: g5, e5, h5, Qg5, Qh4, Qe7, Qf6, Qd6 (Qd6 is maybe a little harsh.).

Obviously terrible: Ke7,Kd7,Ba3,Bc5,b5

Have I missed any?

It looks like black's tried slightly over half the legal moves. Of the bizzare looking lines: 
c6 is presumably an ultra subtle waiting move intending c5 later whilst detering exd5 (but meanwhile it *is* a clear tempo ); Bb4 looks a bit too cheeky really;
Nh6 is perhaps too early (it's rather lost if white goes exd5) and Bd6 could be deemed an amusing attempt to reach a 4.. Ng8 variation!? (However Ngf3 etc are harder to meet.).

Of the potentially 'playable' moves (for some rather loose defintion of playable): 
a5 could turn into some kind of space grab or support a Na6xc5 manouver; f6 is very ugly!; Qd7 is a bit pointless and blocks d7 as a retreat square for the knight and finally Na6 is somewhat strange but does develop and support c5. Of course it could well end up stranded!

I've got a soft spot for 3 .. Bd6/Na6 on grounds of sheer cheek and 3..c6 as it's a 'perfect' waiting move.
But I doubt they're really much good and the quantity of playable lines is enormous anyway