A simple raytracer is a nice and interesting way to learn the basics of a language. You'll probably learn basic data structures, objects, recursion, file i/o etc.
I found Minilight yesterday. It is both more and less than a ray tracer, being a global illumination renderer. It was created as an exercise to learn new languages. Its creator has implemented it in C, Scheme, Scala, C++, OCaml, Lua, Ruby and Flex 2. Others have implemented it in Python, Java, F#, C#, and Clojure.
