Try 1. d4 c5 opening when white plays 1.d4. White will probably take and then just open up with 2. dxc5 e5. I believe this is called the Benko. I also often find that black can sacrifice the c pawn at any time and be alright, except for in endgames. I plan to make several 1. d4 c5 online challenges if anybody is open. 

No, the benko is something totally different. dxc5 is not the best move, just d5 leads to a closed game that often gives him chances for the advantage, but black gets counterplay.

You will be surprised how little people do 1. d4 c5 2. d5. Plus, if that happens,

2. ... e5 3. dxe6 dxe6. This is a surprisingly amazing game for black. There is another version I learned if White does d5 but I can't remember at the moment.

Yeah, that's true rob, and that's what usually happens in the czech benoni, with a totally different move order (1 d4 Nf6 2 c4 c5 3 d5 e5).

if you like to play c5 against d4 try the tarrasch defense.

Yes, but this is an inferior version of the Benoni, whether Black tries the Czech or another set-up.  White hasn't yet played c2-c4, which move isn't necessary after 2 ...e5 and in fact restricts White's own options.  Instead he can leave the c-pawn where it is, and he is almost playing a tempo up on the usual lines.

I'd play 2.e4.

1. d4 c5 2. dxc5??! This is an obvious error that only a very beginner would make.

1. d4 c5 2. e4 transposes to the Sicilian where white might be playing the Smith Morra Gambit.

1. d4 c5 2. c4 is also a possibility not yet mentioned in this thread.

You'd be surprised just how many people take c5

also, there is no point in c4

Yes I agree that 1...c5 isn't the best way to play the benoni, because it gives white so many more options.

By the way I know 2 dxc5 isn't good, but is it really that bad either? It's sort of like a reversed QGA (black doesn't have to play ...d5 I suppose, but if he doesn't it'll probably be some kind of siciliany structure). It's not like dxc5 loses Loomis, even though it's inferior.

No, 2 dxc5 doesn't lose, but it does give up most of White's hope for a reasonable opening advantage. 

White has the advantage of half a tempo: he moves first but Black always gets to respond.  In order to keep and increase that advantage it is necessary to press it.  Pressure must be kept on Black, he should insofar as possible be forced to respond to White's threats and not allowed too much leeway to pursue his own plans.  One key condition for accomplishing this is maintaining some tension in the position. 

The move 2 dxc5 releases tension.  White has traded his center pawn for a near-center pawn, but hasn't gained in development by it, so it's a net loss (if a barely measurable one).  Black must spend time recapturing the pawn, but will do so in the course of developing, so he loses no time there.  2 d5, in contrast, maintains the tension by avoiding exchanges and gaining space in the center.  But even 2 Nf3 is more logical than dxc5, since after 2...cxd4  3 Nxd4 White has something to show for his trade of d- for c-pawn in his occupation of the center.

Again I totally agree estragon, but Loomis was making dxc5 look like it just gives white a hideous position, which it does not.

2 Nf3 I don't think is that much more logical than dxc5 though (maybe a little). True, the knight comes to d4, but from there it may lose more time if it's attacked; compare that to when something goes on c5, (which takes time to regain), most likely the piece on c5 (queen or a bishop, unless he wastes time with the knight) will be exposed to at least some kind of attack (maybe a3 b4 as in a QGA, who knows, but c5 in any case seems to be a slightly exposed square). The one good thing about the move is that he doesn't have to support his center anymore and opens a line.

So I'm not trying to say dxc5 is good or worth playing, I'm just saying it has its good points, because some people may think black is even better just because white loses a central pawn. But again I would agree that dxc5 offers white no real chances for the advantage, I'm only playing devil's advocate because Loomis makes it look like a blunder.

After 1.d4 c5 2.e4 cxd4 3.Qxd4 Nc6 4.Qe3. 

Normally you would not take the d pawn though.

So what would you play after d4 c5 e4

Some people play d6, I play e5 or Nc6.

Those moves are okay, but I think e6.

Okay then, Try it. Are you planning after that d5 or Nc6?