Programs for a Sorcerer Supreme

Hello, /prog/.

I know the subject is vague, so let me explain:

I'm confident I know some programming languages very well, but I feel my knowledge is lacking when it comes to many others. So I'm looking for programs that can sharpen up my skills. Stuff that requires one to use most of a language's features. What would you suggest?

C - compilers. Device drivers?
C++ - game engines?
Scheme - an interpreter?
Common Lisp - ?
Haskell - ?
Java - ?
.NET - ?
Scala - ?
Python - ?
Ruby - ?

group#A low level languages: C, C++, Assembly - Learn assembly first, dont make the mistake of being another "Teach yourself C++ in 21 days programmer. assembly will make you understand what is really going on.

group#B functional languages: Lisp, Scheme, ML, OCAML, Haskell, Erlang (experimental: Scala, Clojure) - Just pick one and learn it, Scheme is usually the easiest to start out with although some people really dont like parenthesis and will start with Haskell. I personally believe its better to start with Erlang than Haskell as Erlang is sort of a subset of Haskell. Wait till youve learned a conventional functional language before you try an experimental one like Scala or Clojure

group#B scripting languages: Python, Ruby, Perl, Lua - Again, just pick one and stick with it. The advantage of one over the other is really just a matter of opinion and preference.