The root ideas of socialism are dead simple and can be understood by anybody. They haven’t changed since Marx and Engels wrote the Communist Manifesto, which is still the best thing to read if you want to get to know those ideas quickly. Following on from that, Hal Draper’s The Two Souls of Socialism describes the existential struggle within socialism in how to realise its goals: through reform or revolution, top-down or bottom-up?
If you read those two pamphlets you have a good idea of the essence of socialism, but what if you want to dig deeper into Marxist theory? There’s always been the Marxists Internet Archive in which all the great and not so great theorists of every concievable socialist tendency are available in perfect brotherhood, but it’s a daunting challenge to pick out the bits relevant to your interests. You could of course also read Marx’s own book of theory Das Kapital, but it’s hardly the sort of work you speed through in a day’s beach reading.
But have no fear, help is available if you do want to read it. Via The Soul of Man Under Capitalism, comes David Harvey’s lectures on Capital, in both video and audio form. There’s also an accompanying discussion space, Reading Capital.
More interested in a general overview of Marxism? Louis Proyect has put together a series of articles on his blog to form a introduction to Marxism, examining and discussing various classic Marxist works and subjects. There’s also a mailing list.
Want to focus on Marxism in an economic context? Marxist Economics is the place for you, set up by the International Socialist Tendency, which also runs the In defence of Marxism site.
Know more interesting Marxist or socialist theory sites we should be aware of? Bung em up in the comments.