The very first issue of The International Journal of Astrobiology is available free online. There's a very interesting article in it title "Earth-like worlds on eccentric orbits: excursions beyond the habitable zone"
Here's the URL to the PDF:
http://journals.cambridge.org/bin/blade ... &REQAUTH=0
It's an easy to read article detailing the results of a climate simulations of Earth-sized worlds on eccentric orbits. A more recent article by the same authors discusses the effect of obliquity on climate. Unfortunately, that one isn't available for free.
--Chris