Microsoft released SQL Server 2012 on 02-Apr-2012. Those wanting to get their hand on the bits can follow this link. However, it leads to an evaluation copy of SQL Server 2012, which is good for six months
Microsoft changed the product editions with this release. Enterprise edition is now the top-of-the-line product that comes with "unlimited" virtualization rights. The BI edition is a new product for organizations interested in using Microsoft's business intelligence improvements in SQL Server 2012. Finally, Microsoft offers a Standard edition.
On top of the evaluation edition, Microsoft offers a free SQL Sever 2012 Express edition for lightweight use, which can be downloaded here.