The best material for electrical conduction (lower resistivity) is silver. Since it is very expensive, copper is preferred, at an only modest increase in r. To achieve low r, it is necessary to remove gases occluded in the metal during fabrication. Copper is soft, hence it is not suitable for applications where mechanical strength is important. In these instances, the alloy CuBe is used, which has a resistivity close to copper. When the weight is an important consideration, aluminium is used which is half as good as copper. Aluminium also has a higher resistance to corrosion.
When high resistivity materials are needed, like in electrical heaters, especially those that operate at high temperature, nichrome (NiCr) or graphite are used.
Adapted from http://www.virginia.edu/bohr/mse209/chapter19.htm