What is the best response to 1...d5

If white plays 1. e4, and black plays d5
what's the best response? and any lines for white?

exd5 is the best move.  Yes, it loses the center, but it gains a two tempos after a forced 2. Qxd5 Nc3.  After this, the queen must retreat, leaving white up two tempos in development.

Typical book openings give exd5 as the most common/preferred move, and it's what I play in that situation as well.

Also, there's Nc3, which is pretty common.

Less common are e5, d4, and d3.

Definitely, take the pawn, chase the queen.

Oh yeah, here's a typical line:

It's called the Scandinavian Defense, and not an opening I would recommend for Black - the Chess Opening Explorer Database, for example, gives the percentages: 45.1% - 28.7% - 26.3% in favour of White. The normal exd5 can lead to, for example:

2...Qxd5 3. Nc3 Qa5 (the main line) - now a sample line 4. d4 Nf6 5. Nf3 Ne4 6. Bd2 Bxd2 7. Qxd2 Bg4 8. Qf4 h5 9. Ne5! Be6, where White has a solid advantage thanks to his aggressive piece postings and better development.

No RainowRising, black wouldn't move the knight with a white pawn hanging.  2. Nf6 leads to a loss of material, so the 1. d5 was all for nothing.

Two other lines worth considering from the black side:

1.e4 d5 2.exd5 Qxd5 3.Nc3 Qd6

1.e4 d5 2.exd5 Nf6
The idea here is that the straightforward 3.c4 c6 4.dxc6 Nxc6 gives black good compensation for the pawn. White should probably instead play 3.Nc3 or 3.c4 c6 4.d4 cxd5 which transposes to the Panov Botvinnik in the Caro-Kann, more normally reached through the move order 1.e4 c6 2.d4 d5 3.exd5 cxd5 4.c4 Nf6

I personally play the 2.Nf6 Scandinavian as Black, and I love it.

I say move Pawn 3D But maybe thats just me :)

Rainbow, I think it is too dangerous for white to try to hang on to the pawn - as ozzie says, black can get very nice compensation with 3. c4 c6 4. dxc6 Nxc6 with more space and pressure down the d-file which results in easy development while white is quite cramped.
Black might also consider 3. c4 e6!? 4. dxe6 Bxe6 which also gives him good compensation. The idea here is to play Qe7 or Bb4 and Qe7, threatening Bxc4+ or a similar discovered attack, and then play Nc6 and castle long, again with nice pressure.

Most games after 2. ..Nf6 continue with 3. d4 or 3. Nf3 when white will probably play something like d4 and c4, Be2, Be3, Nc3 and Nf3 and O-O. Play here is similar to an Alekhine's defense.

@Alphastar18 good point, that is a great setup against the Nf6 version of the Scandanavian.

the 2...Qxd5 centre counter is actually more solid than most players give credit for. The opening is solid, and easy to learn, but tends to get really boring after i played around 3 games with it

If anyone wants to know more on the 3... Qd6 line of the Scandinavian (1. e4 d5 2. exd5 Qxd5 3. Nc3 Qd6) and many other opening, middle and endgame strategies and tips, consider becoming a diamond member! For an incredibly low cost, 20-30mins of high-quality master video content is added practically daily!

After all my games finish, I think I'll put out some seeks to try out a new opening or two. The ones I've been recommended:

The Berlin (requires study I'm sure since it's topical)
The Scandinavian with 3... Qd6
The Alekhine
The Traxler

To suggest that White immediately gains two tempos is simply wrong. One of the interesting things about the Scandinavian is the almost universal failure to acknowledge that 2. exd5 also loses a tempo. After 2. exd5 Qxd5 3. Nc3 Qa5 (or Qd6) each player has moved one center pawn and developed one piece. No one has gained any tempos yet.

It is true that Black may eventually move his queen again, but even that is often a reaction to White moving his queen knight a second time.

Actually it is called the marshall gambit, and while not a preferred line it is playable, and saves from losing the tempo. Someone said above you lose two tempi, but that isn't the case you only go down one tempo.

Darkphobos, the tempo comes after 3.Nc3 Qa5 White has developed while Black has to retreat the Queen

Okay, sorry about that.  I was thinking that the center pawn was also a tempo, but that was taken!

Thanks for the information about the Marshall Gambit.  I guess that's for people who value tempo over material.

I like a gambit line against Qa5.

The tempo is getting to play d4 right after developing. Also Black's queen out tends to be less valuable than white's knight out. Other than that, the opening is solid and occasionally the queen can be used effectively but that's not certain.