Einstien won his Nobel for work on the photoelectric effect, not relativity, though obviously the latter mattered more.
The photoelectric effect led to quantum mechanics and the associated science and technology. I don't think it's obvious that relativity mattered more. If you judge by day-to-day use, one could plausibly argue that our understanding of quantum mechanics has a bigger impact.
So, he basically described photons as a particle for the first time. That's also ridiculously huge. http://en.wikipedia.org/wiki/Photoelectric_effect Considering they had been generally thought of as a wave before that. (http://en.wikipedia.org/wiki/Maxwell%27s_equations) Setting the stage for a lot of wave / particle duality aka QM theory.
I don't think he used the word photon, but he did describe light as particles, and had (flawed, but that is science) arguments for that (http://www.studyphysics.ca/newnotes/20/unit04_light/chp1719_...)