With all the fancy material out there to make nuts out of it can get a bit confusing. Most low cost guitars (and some expensive ones) come with plastic nuts which is one of the worst materials for transmitting sound.
Graph Tech makes a synthetic ivory material (yes nuts were made out of elephant tusks at one time) that they call TUSQ which makes a good nut and is easy to work. You can buy them with pre-cut slots or in blanks.
If you need a nut that allows the strings to slide through slots such as on a tremolo equipped guitar the Graph Tech graphite material makes very nice nut but the black graphite doesn't look good on vintage guitars and it doesn't last very long. Graph Tech now makes the XL line which is white and made out of a Teflon impregnated material which lubricates the strings as they move back and forth through the slots.
Of all the materials, I find bone to be the overall best choice for a nut if it is done correctly. If a bone nut is cut well and the slots are polished it will not only let the strings slide back and forth without binding up, but it also sounds and looks beautiful. Bone has variegated colors that run through it and every piece is different looking. You can get bone in both white (which is really an off white) and vintage which is a more amber color.
Below you see a new bone nut I installed on a Gibson Les Paul Studio and above it is the original nut which is made out of plastic or maybe Corian. Not only does the bone look better with it's highly polished surface, it sounded better too.
