Common Lisp

Do any of you use common lisp? If so, which implementation do you suggest and why?

What about for just learning to work with the basics? Is one implementation as good as another? I've heard Practical Common Lisp is available online, though I'm afraid to google it because those keywords should turn up a huge number of results... Is that a good book to learn with? Should I use another one? By the way, this is my first Lisp.