Potlucks are a great way to combine community building and green education: try a vegetarian or local-foods potluck and everyone gets involved -- or cook foods from your garden. Movie nights are easy: try the BBC's Planet Earth series, explore Grinning Planet's list or these moving images. For kids: 5 Party Themes.
Making your own decorations is often a huge improvement. Use fruit as centerpieces, such as a fancy bowl filled with lemons and limes. Glass bottles filled with food-dyed water also add a nice touch.
After dark try candles -- choose soy or beeswax instead of petroleum based paraffin. Decorate with plants or flowers from the backyard or your local farmer's market or organic fruit -- then send the decorations home as party favors.