The British Library has a digital copy of parts of the original Communist Manifesto – only 26 are believed to have survived worldwide! It also provides background information on its publication. The library website also has an image of Marx’s original British Library readers ticket.
You can read his classic works, letters and writings free from the Marxist Internet Archive which also provides access to a wealth of other primary resource materials on later Marxist writers worldwide.
Special Marx 200 collection This website has numerous links and articles.