The Large Hadron Collider which is currently being built at CERN. The LHC is planned to start operation in 2005 and it will be the most powerful accelerator in the world with an energy level of 14 TeV in proton/proton collisions.
What the experiments at the LHC will bring is hard to say, but as the measuring instruments of the LEP were more precise than the LEP itself, it is foreseen that new physics answering some of the most profound questions of our time, lie at energies around 1 TeV, five times higher than produced in the LEP, but less than a tenth of the capabilities of the LHC.