Can I use 2 different brands?

I am looking to build a new setup and the motherboard is packaged with Crucial Ballistix Sport Low Profile 8GB 1600.. but the RAM I am buying is G.Skill 8GB 1866.. I can't use both of these to right?

You can, but it might require some fiddling around with the RAM settings to make it work (or it might not work anyway).

Newegg sells the same 8GB stick of RAM separately as well, by the way. Just click on it in your cart.