There is a SQL Server 2012 evaluation edition available for download:
SQL Server 2012

32 or 64 bit downloads are available. An ISO file can be obtained for burning to DVD.
I downloaded the 64 bit edition.
There are three files to obtain:
SQLFULL_x64_ENU_Core.box
SQLFULL_x64_ENU_Install.exe
SQLFULL_x64_ENU_Lang.box

Download the three files into same directory. Run EXE to extract into subdirectory SQLFULL_x64_ENU.
Run SETUP.EXE in subdirectory to install.
The evaluation edition expires after 180 days.
SQL Server Express 2012 is also available:
SQL Server 2012 Express
A new feature in 2012 is the LocalDB, a scaled down version of Express that can be embedded in applications.