Read Higher Order Perl, think it's usable for Python & Ruby as well..

(available as a free pdf now)

http://hop.perl.plover.com/book/

Edit:

Here's the TOC:

    1) Recursion and callbacks
    2) Dispatch tables
    3) Caching and memoization
    4) Iterators
    5) From recursion to iterators
    6) Infinite streams
    7) Higher-order functions and currying
    8) Parsing
    9) Declarative programming