Crossover Cable: an Ethernet cable that is used for NIC-to-NIC and hub-to-hub connections.

Here is what the pin out looks like. Remember only one end needs to be crossed, or you'll end up with a crossed cross over cable... which is just strait though. 

Here are a few diagrams showing the proper crossover and straight through wiring.

Crossover Cable RJ-45 PIN RJ-45 PIN 1 Rx+ 1 Tx+ 2 Rc- 2 Tx- 3 Tx+ 3 Rc+ 6 Tx- 6 Rc-

Some other ways of making a crossover include putting a RJ45 jack back to back with another RJ45 jack basically making a crossover adapter, or 2 port hub. If you take a standard cat5 patch cord and put a RJ45 jack at the other end you  make a crossed network extension cord and also making that cable easer to identify. These other methods are easer for people who don't have a crimp tool to make RJ45 plugs, and therefore most people do one of these.

I have collected some other diagrams of crossover cables, just incase you didn't understand the diagram above.