Illegal Immigration: Who Deserves the American Dream?

Millions of illegal immigrants live in the United States right now, with millions more attempting to cross the border every year.  Are these migrants an unsustainable drain on our resources, or do the economic benefits they provide outweigh the costs?  Do countries have a greater moral obligation to ensure their own citizens are cared for, or do people have an inherent right to be supported regardless of their country of origin?