SQL Server for testing on the web
Check out http://sqlfiddle.com/
A tool for easy online testing and sharing of database problems and their solutions.
You would have to pay for any server you use on the cloud, MS offer SQL Database (the rather vague name for what was known as SQL Azure)
Amazon have also recently started to offer SQL Server cloud hosting.
You could pay for a month's testing and then the database would be deleted.
You could use SQL Fiddle
and run your queries in SQL Server 2008 R2 or 2012 mode:
http://sqlfiddle.com/