Get it at: http://www.microsoft.com/sqlserver

Including new features such as

• Resource Governor for managing current workloads
• Data compression and sparse columns to reduce storage and increase performance
• Transparent Data Encryption and advanced auditing
• Spatial data support
• SQL Server Reporting Services integration with Office 2007
• Policy-based management for enforcing compliance across the enterprise

and a size to fit your needs

• Enterprise - for large scale, business critical needs
• Standard - for small-to-medium scale organizations 
• Workgroup - core features for branch applications
• Express - free edition for desktop and small server applications
• Compact - free embedded edition for stand-alone and occasionally connected applications on mobile and desktop clients