This credit is back for 2009...it was off the books for 2008!
The amount of the credit increases to 30% of qualified energy-efficient improvements to existing homes and the maximum credit is now $1,500. Previously, the limits were 10% and $300 or $500, depending on the type of improvement. This credit is for energy efficient improvements such as windows and doors, insulation, etc. Note that the standards will be higher than before: in order to be "qualified", the manufacturer has to certify that its products meet the new IRS standards, so ask before you install.