Gravity waves travel at "c", i.e., light speed.
Some people, notably Tom Van Flandern and cohorts have advanced the position that gravity must propagate at infinite velocity. Their arguments are based on straightforward--and unfortunately incorrect--interpretations of classical dynamics. These arguments produce the conclusion that if gravity travelled at any finite velocity, the Solar System would be unstable and all of the planets would be accelerated out of the system by the "couple" (of forces) resulting from finite gravity propagation.
This position has been refuted by appeal to both special and general relativity. These theories show that gravity waves will radiate any "excess energy" and hence excess angular momentum, in precisely the correct amounts to keep the planets in their appointed orbits.
--Boris