to give just one example:
consider the _super_ part of superstring theory. super is short for supersymmetric, a novel form of particle symmetry first suggested in the early 70's (i believe).
supersymmetry requires that particles have --- errr --- supersyemmetric partners, but to find supersymmetric partners to particles would require collider energies still some way off: best bet seems to be the LHC circa 2010.
see also:
http://superstringtheory.com/experm/index.html
http://physicsweb.org/article/world/12/10/3
see third of the way down at:
http://www.flonnet.com/fl1803/18030810.htm
see Peskin's comments (technical) at:
http://online.kitp.ucsb.edu/online/mtheory01/peskin/pdf/peskin.pdf
les schaffer