This is for Mac OS X users.
By default, the directory listing in Terminal uses the default color scheme of the current window theme. This means everything uses black text on white, white text on black, etc.
Open or create your ~/.bash_profile file and paste this into it:
export CLICOLOR=1 export LSCOLORS=ExFxCxDxBxegedabagacad
Save and close that file.
If you had Terminal open, exit out of it to make sure you load up a clean session.
Now typing "ls" will show directories and files with their own special colors, similar to what you'd see when using a Linux system.