Top Selling Software in May
The following table summarizes the top 10 selling software titles of May 2008:

On Friday NPD also released the top 20 titles, albeit without sales figures for places #11 through #20. That list is shown below.

We can get some vague sense of how things have changed by comparing this chart to the one from a year ago.
In May 2007, the top 20 consisted of 2 Nintendo DS titles, 5 Nintendo Wii titles, 3 PlayStation 2 titles, 2 PlayStation 3 titles, and 8 Xbox 360 titles. That's a 7-5-8 split among Nintendo, Sony, and Microsoft, respectively.
In May 2008, the top 20 consisted of 4 Nintendo DS titles, 8 Nintendo Wii titles, 3 PlayStation 2 titles, 2 PlayStation 3 titles, 1 PlayStation Portable title, and 2 Xbox 360 titles. That's a 12-6-2 split among Nintendo, Sony, and Microsoft, respectively. Nintendo's role appears to have increased in prominence, mostly at the expense of Microsoft, while Sony's diversity (three platforms) has helped it maintain its share.
This is just a generalization from a single pair of observations, but we think it captures some of the spirit of the market. Keep in mind that the top 20 is really only a portion of the software market. The top 10 can account for 25-45% of the market (in dollars or units), and the figures can vary from month to month.