Here is a small list I put together.
If you get more specific about what you are going to be discussing, I can further help you in points you can raise and material to you seek out. By the way, it is important to figure out what kind of socialists you are debating since they varying to such a degree. I would recommend Alexander Gray’s The Socialist Tradition to everyone on your team so they can ascertain what kind of ideology they follow since Gray’s work covers nearly all of the Socialist schools. David Gordon’s Resurrecting Marx is a look at modern Analytical Marxism. Mises Socialism is a good all around philosophical critique of Socialism and his Theory and History is good against Marx’s historical materialism theory.