Using undocumented stored procedure sp_MSForEachDB and DBCC SHRINKDATABASE command you can shrink all databases on an SQL Server in one line of code
exec sp_MSForEachDB 'if ''?'' not in (select name from sys.databases where is_read_only = 1) DBCC SHRINKDATABASE([?]) '
You may need to add additional checks [skip offline dbs for example]. Test on SQL Server 2005.
