ITIL stands for Information Technology Infrastructure Library, but rather than representing a collection of books on IT, it's really a methodology and set of well-documented best practices for implementing and maintaining IT operations and infrastructures. And it's increasingly popular and widely-used so IT pros with ITIL chops are in growing demand. Learn more about ITIL and related certs in this article.
According to the official ITIL Web site, in fact, "ITIL is the most widely accepted approach to IT service management in the world." The ITIL approach divides IT services and their management into a collection of information and implementation domains (ITIL v2), or into a series of practices (ITIL v3) where individual books, courses, and (in some cases) certifications touch on these divisions. There's also a base-level ITIL cert called ITIL Foundations that requires candidates to understand the whole model, and how the different domains all fit together to provide a comprehensive model for IT service management throughout the entire IT life cycle.
The ITIL v2 domains break out as follows
ITIL v3 covers most of the same subject matter, best practices, and principles but divides them up differently, into practice areas
Both v2 and v3 certifications are available for each of these areas, and there are also ITIL v2 and v3 Foundations and master-level certifications as well, that cover all areas of the model. With as many as half of the world's biggest companies either adopting or exploring ITIL pilot projects, and many smaller organizations, government bodies, and institutions following suit, there are lots of opportunities to put this kind of knowledge to work once you acquire some.
At a minimum, it's reasonable to assert that no one who aspires to IT project lead or management positions should not at least earn ITIL Foundations certification, just to make sure they're familiar with its basic principles and practices. This really is useful stuff, and helps to put all kinds of risk management strategies (disaster recovery, business continuity, and high availability) into perspective, as well as providing a holistic model of how IT fits into and supports a modern organization or business.
FWIW, Pearson offers interesting ITIL cert guides and videos. If you want to learn more, be sure to check them out.