My personal list (mostly imperative languages)

C++: (Complex software with elegance + performance )

  Dart source code

  V8 source code (Same people as Dart)

  LevelDB

  Chrome (the only downside: too much virtual dispatch ->   "javism")

C:

  SQLite

  Redis

  Nginx

  Solaris and Freebsd

Java:

  Rich Hickey implementation of the clojure runtime in Java 
 (it was there in 2009.. maybe now this is in clojure itself??)

Go:

  The Go standard libraries