Good Responses to D4

I know that this topic is probably one of a million here but I am only starting this thread up so it is easier to get a range of opinion on a thread/forum when I am on chess.com than searching through the threads.

What are some good responses to 1.d4 and more importantly why is it a good response to you?

Nf6 there are so many good lines,most grandmastersplay it 

I am a big fan of the Modern defense (1... g6) against almost anything, and d4 is no exception. The reasons I like it are that the bishop on g7(almost always my 2nd move) can apply a lot of pressure in the opening and that many players are unfamiliar with the opening which once you get familiar with the opening you can take full advantage of. Another reason I like 1... g6 is that it is a respectable opening against almost anything from white and the goals of the opening are very similar against most of what white can throw at you.

I will caution that it takes a while to learn some of the basic principles of the opening as they go against some other other openings basic principles, I've been playing it for around a year and still learn something new everytime :)

G'luck trying it out sometime!

QGA is underrated. Beginners just dont know that you have to use a pawn break even if your d pawn is no longer there.

I like the Kingsindian defence. Its such a flexible opening which you can play your whole life and which gives you chances to get nice wins even with the black pieces.

Every mainline opening is a good response, it just depends what you like.  

I like 1...e6 after which you can transpose into many good lines like the QGD (I think even the QGA in certain situations!), Nimzo etc.

I like it cause it avoids annoying things like the Trompowsky :P But you need to be ready to play the French if they play 2. e4. 

I would like to play e6 as I am a French and QGD player. However, I am not keen on the Colle or the Stonewall, so I play d5 to give me the option of playing Bf5.