My friend Tazmine who owns Blooming Rock Development has a post that I like listing the tax credits you can get for energy efficient improvements to your home.

The tax credits are for things like new energy efficient windows, upgraded air conditioning, new roofs, etc.

When I was the director of the state Energy Office, we were always careful to point out that some of these things have a quicker payback than others. The quickest payback comes from new insulation in your attic, water heaters and heat pumps, higher efficiency A/C and just making certain your windows and doors are not leaking badly.

New windows are great, but unless they are really bad, you are not likely to make back what you put in to them for years, as they are so expensive.

However, much of this depends on the situation. I would talk to Tazmine, as she does home renovation planning for sustainability and she can make give you advice based on your entire energy profile.