According to BusinessWeek online, the top business story of 2007 is the state of the U.S. housing market (and related effects on the debt markets worldwide). You can read brief reviews of this and the BusinessWeek to 10 business stories of the year by following this link.
If you're looking for the top D&O story of 2007, Kevin LaCroix, Senior Member of the Management Team at OakBridge Insurance Services has posted his list at The D&O Diary, and interestingly enough his top story is also related to the US housing market. You can view his list and insightful commentary by following this link.