Even though SharePoint 2007 has a wonderful feature of Recycle Bin, its disadvantage is that it does not capture Site Collections Deleted. If we have to restore the deleted Site Collection, get it from the backup and if no backup, forget the site and re-create again.
I hope that archiving of a Site Collection feature is introduced in SharePoint 2010, but in the mean time, we can still use an open source tool, easy to deploy on the SharePoint FARM given by CodePlex.
This tool will capture the deleted site collection immediately and send a mail to the Site Administrators with the name of the person who deleted the site. Also allowing you to restore the site if needed immediately.
Microsoft IT Site Delete Capture LE 1.0