Electron accelerators can be unique sources of THz radiation for probing low energy dynamics in solids.  At the NSLS (Brookhaven Lab) we use both incoherent THz radiation from an electron storage ring source and coherent THz radiation from a photo-injected linac source.  The storage ring THz is coupled to a high-field magnet for investigating spin and cyclotron resonance phenomena, while a synchronized Ti:sapphire laser enables the study of photoexcitation dynamics on a ~100ps time scale.  With this facility, we have investigated a number of material systems including Dirac-like quasiparticles in graphene films, the mixed (vortex) state in superconductors and the recombination of excess quasiparticles into Cooper pairs.  Likewise, the intense coherent THz pulses from the linac source are useful for investigating strong-field properties of materials.  Novel electro-optic effects have been observed and work has begun to study non-linear and ultrafast phenomena in other materials.