Blatant copy-pasta from Wikipedia
1911 Equivalence principle
Discovery of the Atomic nucleus: Rutherford
Superconductivity: Kamerlingh Onnes
1913 Bohr model of the atom: Bohr
1916 General relativity: Einstein
1919 Light bending confirmed
1922 Friedmann proposes expanding universe
1923 Stern-Gerlach experiment
Matter waves
Galaxies
Particle nature of photons confirmed
1925–7 Quantum mechanics
1925 Stellar structure understood
1927 Big Bang: Lemaître
1928 Antimatter predicted: Dirac
1929 expansion of universe confirmed: Hubble
1930
1932 Antimatter discovered: Anderson
Neutron discovered: Chadwick
1933 Invention of the electron microscope: Ernst Ruska
1937 Muon discovered: Anderson & Neddermeyer
1938 Superfluidity discovered
Energy production in stars understood
1939 Uranium fission discovered
1944 Theory of magnetism in 2D: Ising model
1947 Pion discovered
1948 Quantum electrodynamics
1955
1948 Invention of the Maser and Laser - Charles Townes
1956 Electron neutrino discovered
1956–7 Parity found violated
1957 Superconductivity explained
1959–60 Role of topology in quantum physics, predicted and confirmed
1962 SU(3) theory of strong interactions
Muon neutrino found
1963 Quarks predicted = Murray Gell-Mann and George Zweig
1967 Unification of weak and electromagnetic interactions
Solar neutrino problem found
Pulsars (neutron stars) discovered
1968 Experimental evidence for quarks found
1968 Dark Matter theories - Vera Rubin
1970–3 Standard model of elementary particles invented
1971 Helium 3 superfluidity
1974 Black hole radiation predicted
Renormalization group
Charmed quark found
1975 Tau lepton found
1977 Bottom quark found
1980
1980 Quantum Hall effect
1981 Theory of cosmic inflation proposed
1982 Fractional quantum Hall effect
1995 Bose–Einstein condensate found : Wolfgang Ketterle
1995 Top quark found
1998 Accelerating expansion of universe found
1999 Slow light experimentally demonstrated : Lene Vestergaard Hau
2000 Tau neutrino found
2003 WMAP observations of Cosmic microwave background
http://en.wikipedia.org/wiki/Timeline_of_fundamental_physics_discoveries
What's next? Hmm. I think we have a few pretty nice things pop up in the news every week or so. I imagine what's "big" will depend on your field of interest.