SQL Server 2008 R2, it comes with new editions and lot of new features, also supporting the SQL Azure & PowerPivot with Excel 2010. The first info about SQL Server release date (21/04/2010) was on Brent Ozar (blog | twitter) post including info of the new features.
Except Enterprise & Standard Edition, SQL Server 2008 R2 has two new premium editions and they are DataCenter & Parallel Data Warehouse. These two version are especially for the needs of large scale DataCentres and Data Warehouses.
Parallel Data Warehouse
About the price list and for further info about all SQL Server 2008 R2 versions are here