On Lisp is a great Lisp book, but it's not for beginners.
Structure and Interpretation of Computer Programs (SICP): absolutely the best and most complete introductory computer science textbook available. This is used in MIT's 6.001, the intro. computer science course that I took as an undergraduate and taught three times as a teaching assistant, twice as head TA. It is an incredible, comprehensive course.
Frink: a practical calculating tool and programming language designed to help us all to better understand the world around us, to help us get calculations right without getting bogged down in the mechanics, and to make a tool that's really useful in the real world. It tracks units of measure (feet, meters, kilograms, watts, etc.) through all calculations, allowing you to make physical calculations easily, mix units of measure transparently, and ensure that the answers come out right.
GNU documentationin various forms (e.g. Texinfo, nroff, TeX, or LaTeX source and Postscript PDF, DVI, HTML, and Info)
Savannah.GNU.org: a central point for development, distribution and maintainance of Free Software
GNU Lightning: a library that generates assembly language code at run-time; it is very fast, making it ideal for Just-In-Time compilers, and it abstracts over the target CPU, as it exposes to the clients a standardized RISC instruction set inspired by the MIPS and SPARC chips
Graphemica: For people who ♥ letters, numbers, punctuation, &c
Protovis: composes custom views of data with simple marks such as bars and dots. Unlike low-level graphics libraries that quickly become tedious for visualization, Protovis defines marks through dynamic properties that encode data, allowing inheritance, scales and layouts to simplify construction.
NetBeans: the project that develops NetBeans IDE, the full-featured integrated environment for Java Developers and NetBeans Platform, the widely adopted infrastructure backplane for complex desktop applications
PicoContainer: a small, simple container for arbitrary components
Common Lisp Directory: ...a resource for Common Lisp users who are invited to post mostly Lisp related links into the LinkIt section and use/comment the Directory and Knowledge Base in the Directory section
Scieneer Common Lispfeatures support for Symmetrical Multi-Processor (SMP) systems on various Unix based platforms
ThinLisp, a practical dialect of lisp for real world applications. You develop in Common Lisp, you deploy in C. ThinLisp programs are as fast as C, by design. Used for a decade in million line systems.
GIMP, the GNU Image Manipulation Program, whose extension language is Scheme
Impromptu: OSX programming environment for composers, sound artists, VJ's and graphic artists with an interest in live or interactive programming. Impromptu is a Scheme language environment, a member of the Lisp family of languages.
Wafer: a research project which compares the many open source web application frameworks which are available using a common example application
Wotsit.org: the programmer's file and data format resource. This site contains information on hundreds of different file types, data types, hardware interface details and all sorts of other useful programming information; algorithms, source code, specifications, etc.
XWT: XML Windowing Toolkit... lets you write remote applications -- applications that run on a server, yet can project their user interface onto any computer, anywhere on the Internet
YAML: YAML Ain't Markup Language specification, Version 1.1