socialism is the antethisis of libertarianism...
Based on the idea of a collectivist origin of rights, socialism is a system in which the state owns the means of production and of capital for investing in collective projects. there are many conceived forms of this, with the most famous being those of the Utopian socialists who envisioned a world in which all needs were met by the state's planned economy and all action being for the good of society as a whole.
libertarianism, in contrast, is a system based on the non aggression axiom:
"no person shall initiate coercion against another individual"
no exceptions
this goes hand in hand with the concept of private property rights, as opposed to state controlled use of property in a socialist system. the individual, acting upon his own rational self interest, has the right to dispose of this property as he wishes. Murray Rothbard, one of the framers of the modern anarcho-capitalist movement, argued that such natural market tendencies as the need to preserve capital gains into the future, etc... would benefit mankind on a whole, although this, as Rand said, is just a secondary consequence of free individuals acting on voluntary basis under a philosophically just system in which the only function of government is to uphold our rights to person and property.
libertarians hold to the concept of private ownership of all utilities, roads, etc. and are most closely associated with the Austrian school of economic thought, which puts emphasis on the actions of individuals in a free society based on psychology.
Ron Paul, Lew Rockwell, Ayn Rand (though she denied it) and Murray Rothbard are all examples of famous libertarians...
BTW... the libertarian PARTY is a statist organization which does not strongly stick to the principles of laissez faire and non initiation of force... it's just a watered down version of the republican party.
Edit: The Libertarian party - as with any political party in the massive US - contains a broad spectrum of ideology and adherence to party principles. Stating point blank that the Libertarian party is a watered-down version of the GOP is misleading and inaccurate.