There are quite a few different choices...The most common choice is braided parachute cord, it's not expensive and you can get get different colors to match all of your tack. Then there are leather braided reins, other types of braided reins, cotton gaming reins, and it just goes on and on...IMO, the best way to go for a beginner is the parachute cord braided reins with knots on them to know where to place your hands..
Here are a few websites you can browse through and get a feel for what you like.
Like drum said I have a pair of the disco reins and I love them but they faded after just a few uses but they were beautiful when I first got them.
My all time fav are these Braided Barrel Reins
Mine that I have are kind of stiff but its because I got more then a 6 plait, I think mine are the 8 plait. I absolutely love the way the knots are, they are like braided on.