Cape Canaveral does equitorial orbits. Vandenberg AFB does the polar orbits.
The visibility depends upon the orbital inclination targeted for the mission. A launch to a 28.5 degree inclination orbit sees the shuttle climb to the east of the Kennedy Space Center, directly away from the US coast. This orbit allows heavy payloads to be lifted (up to around 29000 kg) taking advantage of the Earth's eastward rotation. For example the Hubble Space Telescope and Compton Gamma Ray observatories were deployed into such orbits. In this case, the shuttle can only be easily seen between latitude 38 N and 38 S. Far less common is a 39 degree inclination orbit (this provides the maximum de-orbit opportunities). Typically used for life sciences/microgravity related missions, in such an orbit the shuttle can be seen between latitudes 50 N and 50 S. For Space Station missions the shuttle is flown to orbits of 51.6 degrees of inclination. From here observers between latitudes 60 N and 60 S can obtain reasonable views. Normally the highest inclination orbit flown is one of 57 degrees in the case of missions with an Earth observation requirement. In this case the shuttle can be seen between 67 N and 67 S. The highest inclination orbit used was 62 deg, for the STS-36 Department of Defense mission. Launch azimuth constraint limitations do apply. Naturally the launch time and time of year will further dictate whether any good passes can be seen.
Launch to the higher inclination orbits can be visible from the east coast of the U.S