OS X Terminal "must have" utilities
Homebrew

The missing package manager for OS X.

It is an amazing package manager, very light and easy to use. KIS Principle, that makes me think of archlinux. Its community is big and very active.
(see also macports which brew doesn't replace completely, I prefer installing packages with brew, but some complex ones are only on macports)
See also brew tap command which provides some missing formulas that can be useful like when you need latest php version &gt; brew tap josegonzalez/php.
(Homebrew has a policy of not replacing system components, but hey, sometimes you have to)