“You can never get a cup of tea large enough or a book long enough to suit me.”
- C.S. Lewis
Learning a new computer language by poking around websites and haphazardly Googling questions hoping for a hit on Stack Overflow is fine. We've all done it, especially when a deadline is looming and we need a solution ASAP. However, there is nothing quite like reading a computer language book cover to cover and really sinking your teeth not only into the syntax of the language but getting a feel for the theoretical basis of the language as well. A good programming book will teach the syntax minutia along with the semantics and theoretical underpinnings of the language.
I can recommend three fairly modern Lisp books that do this well.
If you have decided to embark on a sincere mastery of modern Lisp and want a book to carry around with you to read cover to cover, then I recommend Paul Graham's ANSI Common Lisp. It serves both as a compact reference to the ANSI standardized version of Lisp and a solid tutorial and survey of the language, including advanced topics such as Lisp macros and the object-oriented side of Lisp, the Common Lisp Object System (CLOS). There are plenty of quality code examples in the book that showcase the bottom-up development style of the language and why it is well suited for rapid prototyping. Although the examples are concise, some of the code will bend your brain which is another benefit of studying and writing Lisp code.
Affordable copies of ANSI Common Lisp can frequently be found on eBay at a good price. A brand new copy on Amazon would be much pricier.
If you don't have much time for anything resembling an academic introduction to the language but might have some spare time in a working environment to do some Lisp hacking alongside Python or other scripting languages, then I would recommend Practical Common Lisp by Peter Seibel. This book was a game-changer upon release because it was the first book to really show how one might use Lisp in a modern work environment featuring use cases similar to something you might find with languages like Perl or Python.
Examples include spam filtering, an MP3 database, and HTML parsing. This book dispelled the myth that Lisp was only a theoretical language meant for an ivory tower computer science department. It also serves as another good reference to the Common Lisp language.
Getting your hands on a hard copy of the book is always great but in the meantime, the complete eBook version can be found here: https://gigamonkeys.com/book/
The third book I would wholeheartedly recommend is Land of Lisp by Conrad Barski and published by no starch press. It is another exciting and relatively recent addition to the catalog of Lisp books. If you're thinking of learning Lisp purely for fun, then without a doubt this is the best book to start with. It introduces Common Lisp with down-to-earth explanations and several game examples that harken back to the days of fun BASIC programming books of the 1980s; not to mention there are cool comics and illustrations throughout the book. The author, Conrad Barski, also generously created clip art graphics of a new alien Lisp mascot for the Lisp community to use as it sees fit.
More about the book can be found here: http://landoflisp.com/
Armed with one or more of these three books you will have a good head start into the world of modern Lisp programming.