Originally Posted by fckm

You're thinking of particles again. Stop it
Think about a water wave. You're on a beach, getting a tan, and you notice the waves coming in off the open sea. In this case, the "wave" is a displacement wave traveling through water. The medium is water. So while the water has mass, the actual wave itself doesn't. However, there are fundamental limits to how fast that water wave can travel. The limits are not dependant on the properties of the wave, it's dependant on the properties of the water.
Stop thinking of quantum mechanics. Don't think of particles. Light is not a particle. Think of light as a wave. Light is not a tennis ball flying through the air. A tennis ball flying through the air has mass. Waves don't have mass. Light has no mass. Waves in water have no mass. Sound waves (pressure waves in air) have no mass.
Waves are not "things" which travel through a medium. Waves are chages within that medium.

Have you ever seen one of those stock ticker signs in time square? It's got a bunch of bulbs and you can make words by turning the lights on and off. Imagine letter 'A' scrolling across that board. The letter 'A' is now a wave. The medium is those light bulbs. The wave, the 'A', is made by changes in the light bulbs. But the letter 'A' moving across the sign has no mass. And yet, it can't move infinately fast. It's speed is governed by how fast those bulbs can turn on an off.

Think of Light as being little 'A's being displayed on a giant 3-D sign.