A statically-typed, JIT-compiled dialect of Lisp. I felt that there was a spot between performance and low-level control, and high-level metaprogramming that no language right now occupies (Except possibly Rust, which looks pretty promising).
I'd also recommend Ghuloum's An Incremental Approach to Compiler Construction, and the specially the accompanying tutorial: http://web.archive.org/web/20091005152403/http://www.cs.indi...
I never got far in Lisp in Small Pieces or the Essentials of Programming Languages, I mostly figured things out as I went along.