Some people who I play always play the symmetrical variation, and I don't know how to play it for white.
[fen ""] 1.d4 d5 2.c4 c5
It's really unknown, I've never seen it actually played except for maybe one or two internet blitz games out of ten thousand. But I've looked up some lines for you.
You play 3.cxd5 and now black needs to decide what to do.
The symmetrical 3...cxd4 4.Qxd4 followed by e4 just loses a pawn.
3...Qxd5 allows white to chase the queen, getting a lead in development:
So black plays 3...Nf6. Now a thing like 4.Nf3 cxd4 5.Qxd4 Qxd5 stays completely symmetrical, but white can play 4.e4!.
Fundamental Chess Openings gives two lines, both a bit better for White because of better development:
The symmetrical defense is my favorite, here is how games with me playing as black usually turn out:
This line of play of course requires white to play