1)   SurfX3D 1.0
Surface Explorer 3D plots mathematical surfaces in 3D. User defined surface equations can be explicit, implicit, or parametric. Surface color equations specified by user. Export to clipboard, VRML, POV, DXF, printer. C++ source code included. Free.

 2)   GrafEq 2.12
GrafEq (pronounced 'graphic') is an intuitive, flexible, precise and robust program for producing graphs of implicit relations. GrafEq is designed to foster a strong visual understanding of mathematics by providing reliable graphing technology.