For some reason, I've seen more than a few race cars (whose owners had more money than brains) who used rather large amounts of flex line where hard line would do better (and usually cheaper.) Hard Line should be part of the repetoire. It requires some specialized tools, but the reduced costs and other benefits more than make up for the cost of a flaring tool and tubing bender.
Specs and pictures are planned.
In general, brake and clutch lines should be steel. Copper has fatigue problems and will crack with time.
For fuel and oil lines, Aluminum can be used. A very nice 3/8 inch fuel line is available from Moroso. Note that it should not be used inside the passenger compartment of a vehicle, and should not be used in high vibration areas. Use when in doubt, use stainless steel flex line instead.
In addition to the actual line, you also need ends to allow the plumbing to be connected up. Traditionally, the AN818 Coupling Nut and AN819 Compression sleeve are used in conjunction with the flaring tool to provide an end for a hard line. For larger line (3/8 inch and up) the Tube Mate fitting is available from Earl's that makes this a bit easier (and eliminates the need for a flaring tool.)