Recent versions of Raspbian (which use dhcpcd) allow ssh to work over a link-local address and avahai (which is a zeroconf implementation) enables programs to discover hosts running on a local network.
This means you can plug the Pi into a Computer (with an Ethernet cable) or a local network router and connect without knowing the IP address.
You can easily connect from OS X with ssh [email protected] (the default hostname is raspberrypi)
You can use a crossover cable, but you don't need one (most modern interfaces automatically detect).
I think this answers the question I think you are asking. See How do I set up networking/WiFi/static IP address on Raspbian/Raspberry Pi OS? if you want more detail.
