Now I'm challenging project euler in scheme. Project euler is, with the words at the site, "a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve."
At first, scheme was not comfortable language for me because I have studied scheme only in CS class in university as one of functional languages several years ago. Now I enjoy to solve problems in scheme, using another part of my brain than thinking with procedual language like C.
You can see my works at hatena diary. Although additional descriptions is written in Japanesse, you could understand my program if you are interested in project euler and/or scheme.