Try the various Beginners books (once put out by Icon, now I don't know who).
Check this spot out: http://www.blacksheepbooks.com/catalogue/begin/
They have in the series books on Marx, Stalin, Trotsky, Keynes, Economics, Sociology, Barthes, Foucault, Postmodernism etc. They're great for absolute beginners (especially the younger crowd who enjoy graphic novels or comics), and they have lovely annotated bibliographies for those whose appetites get whetted for more.
Todd