The August CTP of Microsoft SQL Server 2008 R2 is now published: http://technet.microsoft.com/en-us/evalcenter/ee315247.aspx. Give it a try and give us feedback!!!
This release does not have many changes around the Express when compared to SQL Server 2008. But the next CTP will contains several improvements as a result of your feedback. Here are some of the changes that will be in the SQL Server 2008 R2 Express product: