The new features are summarized on https://connect.microsoft.com/SQLServer/content/content.aspx?ContentID=5470

There are many new features, so it depends on what you need. If you store large files in SQL Server, migrated from Oracle and want to use date and time data types, need to encrypt your databases, etc you will definitely want to look at 2008. The nice thing is that it upgrading should be much easier from 2005 to 2008 than it was from 2000 to 2005.

Regards,

Andras