Your HOA may not like it if you put a compost pile in your front yard, or let your lawn go "au natural," but there are some things that you can do to be energy efficient and environmentally friendly that won't get you a fine from the HOA!
Buy Energy Star appliances - these are not the end-all and be-all of the environmental movement, but they are a good start.
Plant HOA approved trees and plants - Planting trees will help replace oxygen and remove CO2. The more you can plant, the better your gift back to the environment.
Use Low Volitile Organic Compound Paints (VOC) - VOC paints are non-toxic and will not pollute your indoor air.
Use LEED-Certified Building Materials - LEED Certifications come in different levels, but it all comes down to how environmentally responsible the materials are. If you are building a home, or addition, think about using a LEED certified builder and LEED certified materials.
Use Mult-Zone HVACs - Buy an HVAC system that is designed to distribute air to different parts of your home and pre-programmed times to keep the parts of the homes at different temperatures depending on usage. The initial cost will be more, but the savings can more than make up for it... and it is better for the environment!
Replace incandescent lights with compact fluorescent or LED bulbs - The bulbs are becoming the norm, but you can still buy the old kind... When given the choice, take the greener compact or LED route.
Make sure that recycling bins are put in common areas with the garbage - By simply giving neighbors the option to recycle, most will!
Start a Green Committee - Join forces with your neighbors to help educate each other on green-options, innovative ways to be environmentally conscious and provide assistance to the HOA in making better decisions.