What is the best move in this spot?

I like g4, with threats of g5 and then h4, and following up with Nd5

.... and after a4? (looks awkward).

p.s. I think White has to play either Kb1 or Bb5 to keep the Knight active (and out of the corner).

Either Bb5, a4 or Qe1. Most likely Bb5..

The correct move is Bb5. This develops a peice and defends the threat.

a4 gets my vote. Bb5 seems nice, but we'd actually prefer a N posted there. a4 allows Bxb3, which damages our pawns a bit and reduces our king safety, but as it exchanges his good bishop for our worst piece -- I'm okay with that.

Thank you all for your input, it was of great help!

Bb5 , or  a4 are moves for white that I think lead to advantage, as white I have often played a4 in such positions and do ok with them. Yes, I am giving black the b4 square but in return cement the b5 square for myself and prevent a4,a3 by black. The exchange of B for N on b3 is not a problem for white as black gives up the 2 Bs, weakens control of d5 and the white kb will soon come to c4.

call me stupid, but whats wrong with simply a3 and blocking it all off (with Nd5-Nxd5-exd5)? 

Yes, i understand the knight will be stuck on a1 for a while, but does it matter in the context of the game? the c-file will come under attack after a while and the knight is a good defending piece

Is my position getting better or worse is the salient question -- or as Silman puts it: What great thing for my position did my last move just accomplish? So, what positive does a3 (allowing him to push a4 and sending the N to a1) accomplish? I don't see any positives. I don't see how you can the N on a1 as anything other than a horribly placed piece. a3 is very bad IMHO.

well, here is how i see it. The point of a3 is to block off the a-file from being opened. The b-pawn can be blocked by the c3 knight which in turn opens up the c2 pawn to double rooks on the c-file. Another option is to block off d5 with a pawn and keep black's dark bishop locked in. Keep in mind that in doing so, you also block black's light squared as well. This effectively limites black to using his rooks, queen and maybe his one knight in a queenside attack.

Meanwhile white can easily swing his forces over to the queenside with moves like g4, h4-h5. It wouldnt matter that the knight is stuck on a1, because first of all, it cannot be chased off that square and c2 is solid as a rock. All in all, black might look more active, the truth is black is just more forward. There is nothing in the queenside that he can exploit after a3 (that i can see at least)

Not when i posted above, but if you really really want to avoid Na1, the only clear alternative is :
1. Qf2 Qc7 2.Bb5 Nc6 3.Kb1 h6 (to avoid opening up the g-file all of a sudden) 4.h4 Nb4

This looks roughly equal, but as i mentioned before, there is no real venom in black's attack.

 How can a C class player be "sure" of anything ? I am not sure at all that any of these moves ( let alone all of them ) will end up a draw , even with best play. How can you be ? In any event, we are talking about games between humans anyway and we all know 2 humans playing together are NOT likely to find the " best play " . Maybe if Rybka 3 is playing both sides.... maybe then most of the choices lead to a draw ? What about if one is running on better hardware than the other ?  Still all draws ?  I think engines can be great in helping us in our chess but I think they can also become a huge crutch as well. We all need to be careful that we use engines as tools and not as our masters.