After much anticipation the CTP 5 (Community Technology Preview) of SQL Server 2008 is available.
This CTP includes the first look at 2008 Express Edition. The Express Edition as well as the x86, x64, and IA64 releases can be downloaded from http://www.microsoft.com/downloads/details.aspx?FamilyId=3BF4C5CA-B905-4EBC-8901-1D4C1D1DA884&displaylang=en.