SpaceX in a few more years should be able to do human transportation to orbit. Virgin Galactic is for space tourism and doen't fulfill any of the roles the shuttles were used for. When the shuttle retires, there really isn't anything else (in the US) that comes close to replacing it.

Why should SpaceX be the only competitor who succeeds in the next few years?

http://en.wikipedia.org/wiki/List_of_private_spaceflight_com...