Sometimes people like to use misleading numbers for the speed of propagation down a waveguide (ie: cable). The simplest to talk about is a rectangular waveguide, a rectangular shell made of an excellent conductor. What we care about is the motion of the waves along the axis of the waveguide, but a plane wave front does not propagate along the axis. Instead, the wave front bounces back and forth along the walls, at an angle to the waveguide axis. Since we are only concerned in the propagation along the axis of the waveguide, we can get misleading velocity values. The wavelength is spread out at an angle to the axis, as such, the apparent wavelength along the z-axis is shorter than the actual wavelength. So the apparent velocity of the phase front of the wave along the z-axis is larger than the actual velocity of the wave. So when people talk about the guide phase velocity, the actual velocity reported is not the velocity of energy and it can actually be greater than c. The actual velocity of the energy (or information) of the signal lags behind the phase front and travels at the group velocity, which is always slower than light. We can think of the phase front as being a carrier signal while the group is the information modulated into the carrier. The carrier signal travels faster than the information, and can travel faster than the speed of light. But since the carrier signal does not transmit any energy or information, then this does not result in any violations.
When we talk about radiation, any electromagnetic radiation will travel at the speed of light. For example, gamma rays or x-rays. These radiations are simply photons with high energy. Other forms of radiation, like beta or alpha, transmit elementary particles like electrons or neutrons and protons and thus must travel at speeds less than c.
And as TuxDave said, electrical signals like currents are the result of electromagnetic waves (and electromagnetic waves are the result of currents, yay reciprocity!). As such, they do travel at the speed of light. But due to the fact that light does not travel as fast as c inside a medium other than a vacuum, and due to the fact that it does not always propagate exactly along the axis of our waveguide, the actual speed of the signal is going to be less than c and less than the speed of light in that material.
EDIT:
Electrons do not travel at the speed of light since electrons have a non-zero mass.
Electrons are not the mechanism by which electricity flows. Electricity flows as a result of electromagnetic waves. So as soon as an EM wave reaches a point on a conductor, it is going to excite currents there. However, as I stated, in a waveguide, EM waves do not flow perfectly in the direction of the waveguide, the generally bounce back and forth and thus the velocity of information is going to be less than the actual velocity of the wave in the waveguide's material. Other factors are due to the fact that our electrical devices generally do not react to the EM wave, but to the electrons that flow because of it. In that case we are limited to the velocity of the electrons, but for simple transfer of information down a wire or a trace, that mechanism is from the EM wave. A signal is information, so it depends on how we are transfering that information. So when transfering down a wire, the EM wave transmits the information, only at the device do we start using the electrons to receive and interpret the information.