You'll pay: Anywhere from a few hundred bucks for enough batting for the attic to several thousand for a whole-house upgrade.
You'll save: Up to 15 to 25 percent on heating and cooling.
Why do it now? "Virtually every home needs more insulation," says Paul Scheckel, a senior analyst with the Vermont Energy Investment Corporation and author of The Home Energy Diet.
If the batting in your attic is less than a foot thick, you'll benefit by adding more.
What to look for: Qualified products must meet standards established in the 2009 International Energy Conservation Code. Healthier home options include formaldehyde-free fiberglass batts and cellulose-based spray foam that fills nooks and crannies.
Bottom line: Insulation, when paired with sealing air leaks, is probably the most-bang-for-the-buck of all efficiency measures. Even without the credit, your payback period may be as little as a year or two. Many state governments and utilities offer incentives, too—in some cases rebates of up to $750.