You should check out Darius Bacon's "ichbins", which is a compiler for a small Lisp dialect, targeting C, in just over 6 pages of code. The advantage it has over most toy compilers is that the language is complete enough that the compiler is written in it. (The tarball also includes an interpreter to bootstrap the thing.)
There's more stuff about what I found useful in learning to write a compiler on my Ur-Scheme web page.
