I've been utilizing the reports for years to help clients decide what improvements make sense for them. This report compares the average cost for 35 popular remodeling projects with the value those projects retain at resale. More importantly it breaks down those projects and values based on location. Remodeling Magazine does a great job of compiling this data very year and is widely acclaimed. Here is the report for the Greater Seattle Area. But you can also get reports for most metropolitan areas of the US here but clicking through to it from this map. You'll need to register and give them an email address. But after that you can download the PDF and print it or keep it for your future use.
Something new this year is the iPhone App version of the report, which gives you the data from past years back to 2008 on the go.You don't get all the charts and extra info i the app, though. I imagine in future years they'll have an iPad version will all the info along with how to videos and references too.