Historically there are only two types of motion blur, 2d and 3d. The 2d one is post processed and the  3d one is done at rendertime. 3d motion blur is much more accurate but takes a lot of time to render.

Two years ago, Doug Sweetland gave a talk at Annecy where he explained how much effort it took to achieve a good looking motion blur and I would like to share with you some screenshots I took a while ago.