The novel neutral nickel complex with the extended TTF dithiolato ligand, trimethylenedithiotetrathiafulvalenedithiolate [tmdt(2)- = (S6C9H6)(2)(-)], have been synthesized. The single crystal of [Ni(tmdt)(2)] was metallic down to 0.6 K. The crystal structure and electronic band structure calculation showed [Ni(tmdt)(2)] is the first single-component molecular metal with three-dimensional Fermi surfaces. Metallic behavior was also found in the crystal of an analogous molecule, [Ni(dmdt)(2)][dmdt(2)(-) = dimethyltetrathiafulvalenedithiolate]. Similar highly conducting systems, [Au(dmdt)(2)] and the molecular conductor with localized S=1/2 spins, [Cu(dmdt)(2)] were also prepared.