It really depends on what runtime you're targeting. If you're targeting the JVM, CLR or Javascript then you might want to check out Clojure. It'll let you interoperate with libraries in each of those environments, which you'll find useful.

If you're looking to create a stand-alone executable and have C/C++ libraries you'd like to use then SBCL or Racket may be more useful to you.

I started with Common Lisp and PG's online book On Lisp. http://www.paulgraham.com/onlisp.html