There's at least one good thing about falling home prices -- they make housing more affordable.

In the first three months of 2009, nearly 73% of all homes sold were considered affordable for families earning the $64,000 national median income, according to the National Association of Home Builders/Wells Fargo Housing Opportunity Index (HOI).

That's the highest percentage in the 18 years the index has been published.

The primary reason is that home prices are falling across the country. They fell an average of 20% from their 2006 peak through the end of 2008, and are expected to drop another 15% to 20% this year.

As a result, the number of homes that the median-income family can afford has steadily risen over the past couple of years, from 53.8% in the first three months of 2008, to 62.4% in the final three months of 2008, to the record high of early 2009.

Indianapolis was the most affordable major housing market. Almost 95% of all homes sold were deemed affordable to households earning the area's median family income of $68,100.

The city has been the most affordable market in the study for 15 consecutive quarters.

Other affordable major metro housing markets include Youngstown-Warren-Boardman, Ohio-Pa., and Akron, Ohio.

The New York-White Plains-Wayne, N.Y.-N.J. region -- where only about 21% of homes sold in the first quarter were affordable to those earning the median income of $64,800 -- was deemed the most unaffordable area.

Here's how the median sales prices in more than 140 markets have changed over the past year.