His most recent book -- Liberty and Tryanny -- arrived in 2009 to massive acclaim (it has since sold over 1.2 million copies). Jeffrey Lord of The American Spectator called it "The Book That Changed America"; it was a common sight at Tea Party rallies during the fight against President Obama's brand of socialized medicine.
Since that time, Levin's hinted on his show about his work on a new book. Reportedly completed in July, its title and subject are embargoed until the week before its release. That said, I've gathered enough information from his circuitous references to offer an educated guess.
Title: From Democracy to Despotism
Subtitle: The Left's Fatal Assault on Individual Liberty
Description: As our society frays thanks to the machinations of Barack Obama and Democrats in Congress, we would be well-served to review history. The strategies and tactics of the modern Left are not new; we have seen these machinations before and we must recognize them today.
From Russia's bloody 1917 revolution, to Mao's "People's Army"; from the Palestinian elections of Hamas to Mugabe's Zimbabwe; the world has seen populist and democratic movements many times before.
Most importantly, the Statists of the Left use the democratic process itself to destroy government and the civil society. Most recently, Saul Alinsky (the father of modern community organizing) and Columbia Professors Cloward and Piven have articulated strategies that undermine the American republic from within.
The bulwark standing in their way is the United States Constitution. As the Left's termites eat away at our legal foundation, it's incumbent upon patriotic Americans to learn from history's lessons and politically obliterate the infestation of those who mean to unravel our society.
Whether or not my prediction is accurate, I can say with confidence this about Levin's next book. It will be great.