I am starting to play competitive level chess and have lost to two players who played D4 as their first move... I know we could play along to the coming Queen's Gambit which often throws me off as I have heard that its a powerful gambit should it be accepted, which makes me decline it... So D4 kinda throws me off my game. What is the best or rather easiest defense to learn to counter it...

If it helps, White I play King's Gambit and/or King's Indian Attack

Black against e4, I play French Defense (Language of Love) or Najdorf Sicilian (If I thinks my opponent knows the Sicilian as it only pisses me when they don't know Sicilian and once again I don't know how to continue)

I'll look up the Modern... as for King's Indian Defense.... I have taken a look at it... but I find its too passive as I like King's Indian Attack due to its possible attacking capabilities... Thanks though! =D

I saw a video on it... isn't it just responding to what black does... like you don't get to push on the offensive?

Hmm looks like I'm taking anther loook at it =D

The King's Indian isn't exactly "aggressive."  It's a counter-attacking defense.

Black develops fast, solid, and small.  Which means that if white wants to stake any kind of an advantage, it's going to have to be a space one.

Once white extends himself, if all goes well for black, he should be well poised to capitalize quickly on any OVER-extensions with his harmonious development.

To me, an aggressive defense is something like those lines of the Slav or Semi-slav that try to grab material and/or space on the queenside, and then consolidate it.  Or the Albin or Budapest, that cede material for attacking chances.  Or even the Leningrad Dutch, which says that you want to pursue a KID-ish attack, but without waiting to see if or where white overextends.

As for what's "best?"  Well, nothing is, really.  But if you felt like you HAD to make a case for one defense, you'd probably want to go with either the Semi-slav or the QGD...just because those are the ones the best players in the world seem to have settled on most regularly...or the Nimzo, which many of them I'm sure would play if they were ever allowed to.

XiXax, what's your rating?  if you are below 1600, I suggest you concentrate on tactics and endgames and play the opening as you go along.  I doubt you lost the two games because they started 1.d4.

well considering you seem to be aggressive I have two options first, the benko gambit

I've just began studying the benoni defence, I'd recommend it if you're an aggressive player.

I myself, as a more defensive player, prefer the Gruenfeld, King's Indian and Nimzo-Indian defences.

I'd most certainly recommend 1 ... Nf6 as a response to 1. d4.

Cool guys, thanks =P

I'm planning to look into the KID more soon, as I'm getting bored of the Benoni, and it's a bit too helterskelter for all situations.

The KID isn't a defensive opening at all, but can be very theoretical. Check out this recent game where Nakamura downed Gelfand with what was probably some stonking home prep:

 

Right here:

http://www.chess.com/forum/view/general/the-schmidlap-maneuver

It seems you like agressive openings. A few suggestions might be the benko gambit, grunfeld, or KID. However, don't rely on your openings to win the game. Even though most players think it, the opening is rarely the reason to blame for losing.

True... But openings help =D For instance, not knowing Scholar's Mate would pwn you before midgame even begins

King Indian is same setup as Pirc defence. You can use it almost vs anything. And it is passive defence.

And for OP, you HEARD about Queens Gambit??? Man, you have bigger problems than 1.d4!

I had a similar problem with 1. d4. Couldn't find a reply (as black) which suited me, that was also easy to learn. Then I saw this article on the Chigorin defence by GM Gserper:

http://www.chess.com/article/view/openings-for-tactical-players-chigorin-defense

This suits my style! - black ends up with open play very quickly - so I'm trying it out. I think it is important to play an opening that suits your style, rather than something just because it is strongly recommended. I would never play the King's Indian Defence because I don't like fianchettoing my bishops, but that's just me.

Playin black one move behind so it can b tricky to find a system. Play em all blits for half a year and go deep with the ones that gives u a sence of flow

If you like the French, my suggestion is to try the Nimzo-Indian, you often get a very similar type setup.

Also dont forget to talk with the pieces and ask where they would like to go