Depending on what you need it for, I'd just use a poly plane.

I'd make it 4 divisions by 4 divisions, giving you 5 vertices in each direction. I'd grab the 3 in the middle on one side and scale them in, till they were about the width of the crease I wanted. Then, I'd select the row of verts in the middle of these 3 rows and move them down a bit, giving depth to the crease. After that, it's just a matter of adjusting them from another angle until you've got the shape of crease you want.

Here, like this -
-Simon.