Microsoft recently released the first service pack of SQL Server 2008 R2 for it’s RTM as well as Express Edition. To learn what’s new in SQL Server 2008 R2 SP1, check the What's New Section in Release Notes
Note : To upgrade SQL Server 2008 R2 Express Edition, you need the SP1 of Express Edition or Express Edition with Advanced Services.
SQL Server Denali CTP3
Microsoft also released CTP3 of SQL Server’s next version code-named Denali. You can download SQL Server Denali CTP3 over here. Here are some download links
Microsoft SQL Server code name 'Denali' PowerPivot for Microsoft Excel Community Technology Preview 3 (CTP 3)