http://ece-www.colorado.edu/~siek/ecen4553/ – a course teaching compiling python. Has assignments and links to resources (like info about x86 etc.)

http://www.tinypy.org/ – small python implementation. register-based vm inspired by lua, own gc

http://code.macournoyer.com/tinyrb/ – small ruby implementation, boehm gc

http://code.google.com/p/v8/ – v8, fast JavaScript implementation, compiling directly to native code from parse trees, own gc, C++, embeddable, New BSD license

http://piumarta.com/software/lysp/ – really small lisp implementation, boehm gc or its own, MIT license

http://github.com/why/potion/tree/master – potion, jit compilation, vm based on lua, used 'id’ object model, gc is reference counting, MIT license

http://www.complang.org/ragel/ – compiles FSM from regexpes, can be used for lexical parsing, used by tinyrb

http://www.hwaci.com/sw/lemon/ – lalr(1) parser generator, like yacc, used by tinyrb