Democratic Socialists of America
Socialism is defined as "the collective ownership and control of the means of production." Social democrats combine workplace democracy with government democracy to achieve this end.
The Anarchist FAQ
This site explains anarcho-socialism. Firms would practice workplace democracy, but would cooperate or compete on an otherwise free market without any centralized government at all.
Co-ops are worker-owned and controlled businesses, and are thus the building blocks of socialism. There are thousands in the U.S., and they are more profitable than private-owned firms.
Another excellent introduction to co-ops.
Employee Ownership and Corporate Performance
This site contains information on how Employee Stock Ownership plans (ESOPs) and participative management generally boost profits higher than other companies.
The Noam Chomsky Archive
He's an anarcho-socialist, not a liberal, but the New York Times calls him "the most important intellectual alive!"
Green Parties of North America
Not many people know that the Greens are anarcho-socialists. This website explains their platform.