Practical Common Lisp
Ok, So for what I remember, the programming language I have the most fun with was by far Lisp. At university I learned Pascal, C, JAVA, Smaltalk, APL, FP and Lisp. I just can say that LISP was really fun to work with. It was all about thinking A LOT and only after a lot of thinking writing three lines of code (function name, single instance condition and recursion).
I'll give it another try.