The best description of Lisp lies in the following quotes:

    "Lisp has jokingly been called "the most intelligent way to misuse a computer". I think that description is a great compliment because it transmits the full flavor of liberation: it has assisted a number of our most gifted fellow humans in thinking previously impossible thoughts."
    - Edsger Dijkstra, CACM, 15:10

    "Lisp is worth learning for the profound enlightenment experience you will have when you finally get it; that experience will make you a better programmer for the rest of your days, even if you never actually use Lisp itself a lot."
    - Eric Raymond, "How to Become a Hacker"

    If you  really want to know what Lisp is about, you could read the following articles:

• "Why Lisp?" by Peter Seibel
• "Why Lisp?" by Peter Norvig
• Articles  from Paul Graham
• "Beating the Averages"
• "Revenge of the Nerds" 

•   Pascal Constanza's Highly Opinionated Guide to Lisp
• Common Lisp Survey by Daniel Weinreb 

    If you really want to know what is Lisp, you have to start from the roots, with this two articles:

• Paul Graham: The Roots of Lisp
• Guy L. Steele Jr. and Gerald Jay Sussman: The Art of the Interpreter or, the Modularity Complex (Parts Zero, One and Two)
  

    Now if you want to learn Lisp, you could start with this books:

• Ansi Common Lisp by Paul Graham (not free) 
• Practical Common Lisp by Peter Seibel
  
• On Lisp by Paul Graham
• Common Lisp: An Interactive Approach by Stuart Shapiro
  

    And if you need a Lisp implementation (software) i recommend:

• LispWorks Personal Edition (free - IDE)
• Allegro Common Lisp Express Edition (free - IDE)
• SLIME (The Superior Lisp Interaction Mode for Emacs)

• CMUCL (Carnegie Mellon University Common Lisp)

• SBCL (Steel Bank Common Lisp)
  

  And the place for all Lisp resources is cliki.net