On political theory in general, see the homepage of the 'Foundations of Political Theory' section of the American Political Science Association. Among other things, it will give you access to a wide range of key journals.
The Political Theory Daily Review is a portal weblog that provides links to the latest news, publications, and reviews covering all fields of political theory and political philosophy.
For Marxist literature.
The best source on Bentham, this is the website of the Bentham Project at University College London.