In class I have mentioned that in retrospect, Albert Einstein should have won 5 Nobel Prizes, had he lived long enough so his ideas and theories could be thoroughly tested. He won his in 1921 for his work on the photoelectric effect, which is really based on his theory of the photon. No one in that era was thinking of treating light as a true particle except Einstein, so it was the true birth of quantum theory.
But obviously he also deserved a Nobel for Special Relativity. It has fundamentally changed the way we think about space and time, mass and energy, and led to the development of matter waves. Einstein may have shared a prize, had it been given, with Lorentz, who had made major theoretical contributions and ideas that Einstein finally derived and put into a full framework. In fact, he could have easily shared the Nobel that Louis de Broglie won for matter waves, and may have been overlooked at his contribution and influence on de Broglie's work.
Then there is General Relativity. This is Einstein's masterpiece, and he essentially worked alone on it. No one else was even dreaming of warped spacetime and all the implications coming from this concept - and now we have much confirming evidence that his ideas are correct.
Einstein laid down the theory for stimulated emission, which is the foundation principle for the construction of the laser. And lasers have applications seemingly everywhere in our generation.
Then there is Bose-Einstein condensation, which Einstein predicted in the 1920's. This state of matter was confirmed in the 1990's. The basic idea he recognized was when bosons are at very low temperatures, they are more like waves than particles, and can occupy the same quantum state.
Einstein also had a major influence on multiple dimensions. He developed the notion of 3-D space to 4-D space-time in his relativity theories, which then led others to think about adding a 5th dimension to account for electromagnetism (Kaluza-Klein theory), and now there are 11-D string theories trying to unify all forces and particles together in a single theory - a so-called unified field theory. Where did this concept come from? Well, Einstein! He thought we should be able to create a single theory for all particles and forces, and he was unable to do it. But the idea is alive and well. Then there is the cosmological constant, which he famously said was his 'biggest blunder,' but now the concept of an anti-gravity force may be correct as we try to figure out why some distant galaxies are accelerating in their expansion rates (now we called this 'dark energy').
Oh, also in 1905 was Einstein's theory for Brownian motion, which effectively laid down the mathematical theory for molecular motion. This is a major contribution to statistical physics.
Wow, that is A LOT from one person! Here is another article talking about Einstein's legacy and the number of Nobel Prizes he deserves.