we couldn't afford to go 100% green (let's face it, you need mucho green/$$ to be green) but we spent a good chunk of our budget on a few 'sustainable' items
"cool roof" by duro-last (energy star-rated, 20+ years lifetime, recyclable materials)

Icynene (spray foam insulation a ceiling)

lime plaster (reabsorbs most of the CO2 during the curing process, recyclable, used for centuries in europe due to its long lifespan)
rain screen with VaproShield