Can massless particles travel at speeds other than light speed?

[Tail]

To my knowledge, gravitation travels at the speed of light.

 

[sdeliver645]

Generalization

One could make the generalization that all massless particles travel at the speed of light. They have no choices, one could argue (correct me if I am wrong), due to the symmetry predicted by special relativity. So, this would include a few force carriers, such as:

EM force carrier: photon
Strong force carrier: gluon
Gravitational force carrier: graviton(?)

Does not include the carriers of the strong force, the W+, W-, and the Z0. They have a NON-ZERO mass.