Here's an article about an interesting study done on the impact of illegal workers on wages and consumer prices. Illegal workers depress wages by about 40% in the farm industry and significantly in other industries as well, but affect prices very little, maybe 5% at the most. This will probably be big grist for the anti-immigrant mill.
The study compared what the wages in an industry would be if the illegals disappeared. The huge gap in the study, of course, is that no one calculated what the wages would be if the illegals were replaced with legal immigrants instead. Also I don't know whether the impending hike in the minimum wage will affect things (the Senate seems set to approve the hike to $7.25 now that the House has shown it's okay with adding in the small-business tax breaks). Certainly the fact that the illegals aren't subject to the minimum wage in the first place affects wages.
My support for liberalized immigration laws has always been moral rather than economic, so this study doesn't really affect my stance at all. But it'll be an interesting point of debate for both those who favor liberalization and those who favor a return to 1925-style policy. It could be taken either way, really.
Link via this quasi-self-Godwining yet still interesting Daily Kos post.