Optical metamaterials are rationally designed and manufactured materials built of nanostructured unit cells, or ‘artificial atoms’ much smaller than the wavelength of the operating light. These materials can be engineered to exhibit optical properties beyond those achieved with naturally occurring materials. The field of metamaterials has been gaining momentum over the past several years, as it continues to provide new fascinating ideas promising a variety of exciting applications including super-resolution microscopes, extremely efficient light concentrators and invisibility cloaks. In most metamaterial devices, noble metals (primarily gold and silver) have long been used as the constituent material to make subwavelength building blocks. But metals suffer from high optical losses that are much too large to create practical and robust metamaterials devices. In addition, optical properties of metals can not be tuned and these materials are not compatible with standard semiconductor technology. A recent approach that could unlock the technological potential of plasmonics and optical metamaterials is to look for alternative plasmonic materials that have a negative real part of dielectric permittivity. Here we provide an overview of plasmonic materials and focus mainly on doped semiconductors and transition metal oxides that could allow realization of novel transformation optics and metamaterial devices with greatly improved performance operating at near infrared and visible frequencies.