Thanks for the pointers ;-) I've already studied Scheme a little bit and am aware of the beauty of functional programming languages. I'd give the reference to the Purple Book if it wasn't already mentioned by another member.

I'm also interested in Objective Caml since the time I've learned it was used to design MLDonkey (I was impressed ;-). By the way the online Caml book from O´Reilly: Developing Applications with Objective Caml looks quite cool. I must find time to read and study it :)