The progressive case for Wal-Mart (pdf), featuring much data. (Hat tip: Eric.) The bottom line:

WalMart's low prices help to increase real wages for the 120 million Americans employed in other sectors of the economy. And the company itself does not appear to pay lower wages or benefits than similar companies, or to cause substantially lower wages in the retail sector. Although there may be a dispute about the magnitude of the cost savings for consumers, no one disputes that they are large. In contrast, the effect on workers is relatively smaller and far from obviously negative.