... or textbooks ... String Wiki includes a lot of useful links for people learning string theory. But let us discuss some basic sources here, too.
Polchinski in paperback. Joe Polchinski, the father of D-branes and many other things, has completed the standard modern graduate student level textbook of string theory in the late 1990s. It offers a detailed and perfectionist treatment of conformal field theory, perturbative string theory, and a sketchier but still invaluable presentation of algebraic geometry and non-perturbative physics. Two volumes.
Green, Schwarz, Witten. The graduate level textbook of three heroes of superstring theory from the 1980s presents perturbative string theory in a more heuristic, intuitive way, and it dedicates more space to differential geometry, light cone gauge, and other topics than Polchinski does. Two volumes.
Becker, Becker, Schwarz. This is an excellent modern update of the books by Green, Schwarz, Witten that includes the newest material including flux compactification and the advanced aspects of black hole thermodynamics in string theory.
The book will be released by the end of the year. If you pre-order from amazon.com, they guarantee the lowest price in the case that they will reduce it. Highly recommended! We will discuss the book more in the future.
Barton Zwiebach's course. Barton Zwiebach wrote this book based on his award-winning MIT undergraduate course. It is not only a readable elementary introduction to string theory including advanced topics such as the intersecting braneworlds, but also an excellent set of exercises in mechanics, electromagnetism, and quantization.
Michael Dine's phenomenology Bible. The new book by Michael Dine, a leader in superstring phenomenology, will appear around January 2007. Again, you may pre-order it with the same rules. It is a pragmatic treatment of SUSY theory, SUSY phenomenology, astrophysical bounds, technicolor, dozens of other nice things, and practical features of string theory that will answer 90% of your questions from this arena. We have needed such a book for a long time. It will be mentioned later.
Tomás Ortín. This book is focusing on those aspects of string theory that are accessible to the general relativists, especially the solutions of the low-energy effective equations of motion (GR and SUGRA). In this direction it is very detailed. As a textbook of string theory it might look incomplete.
Mirror symmetry. This book by eight well-known experts covers not only mirror symmetry but probably everything that a theoretical physicist needs to know today before she starts to use higher-dimensional geometry properly. It's a wish of many people like me to learn all these sheaves and fans properly one day.
Elias Kiritsis. This 608-page-long book, to be released on April 1st and sold for $65, is the most concise text among those that are covering virtually everything about the introduction of string theory.
Gasperini and Maharana. This 1000-page book to be released around January 2008 celebrates Gabriele Veneziano's retirement from CERN. Veneziano is the discoverer of the first string-theoretical formula. The chapters from many authors discuss the early days of string theory in the late 1960s, non-perturbative QCD, more modern string theory, duality, and string cosmology, including pre-big-bang cosmology, brane inflation, and other scenarios.
Luis Ibanez and Angel Uranga wrote another textbook on string phenomenology in January 2012:
More special literature can be found in Donald Marolf's resource letter.
See also the 2012 explosion of stringy and supergravity books.
There exists a similar list of some quantum field theory textbooks and topological introductory books.