Here is my replicate-able key/wrench that I use to build my RepRap Prusa Mendel at the moment. It takes standard hex bits and has also got a M8 nut wrench in the center. It can take pretty much load, that depends on how well your print went.
Mine is printed on the UP! 3d printer.
Print and enjoy!
For UP! users, to remove the support structure, remove the vertical support first and then just snap the horizontal support downwards with a pair of pliers and it usually comes out easily in one piece.