A new class of surface plasmon waveguides is presented. The basis of these structures is the presence of surface plasmon modes, supported on the interfaces between the dielectric regions and the flat unpatterned surface of a bulk metallic substrate. The waveguides discussed here are promising to have significant applications in the field of nanophotonics by being able to simultaneously shrink length, time and energy scales, allowing for easy coupling over their entire bandwidth of operation, and exhibiting minimal absorption losses limited only by the intrinsic loss of the metallic substrate. These principles can be used for many frequency regimes (from GHz and lower, all the way to optical).