Available under a Creative Commons Attribution-ShareAlike License:

http://www.marxists.org/archive/marx/works/1848/communist-manifesto/

One of the most influential political tracts ever published this short book succinctly explains the aims and purpose of the Communist League of the 19th century, giving the author’s theories of the class struggle which they assumed would inevitably lead to world wide communism.

Full text available at Project Gutenberg too:

http://www.gutenberg.org/files/61/61.txt