Site Recycle Bin (formerly known as: Microsoft IT Site Delete Capture) Enables administrators to create a snapshot of site collections and Webs as they are deleted through the SharePoint user interface, the SharePoint Administration Tool, SharePoint 3.0 Central Administration, or SharePoint Designer.
By default this tool will only backup sites created from default Microsoft site templates.
Refer here for more info: https://sharepointconnoisseur.blogspot.com/2011/04/tips-and-tricks-for-site-recycle-bin.html
One important point to ponder here is: If you want to delete any site collection, you have to do it from WFE, and Not from CA server. otherwise this tool will not allow you to delete.
Very handy! Download it from the URL: http://governance.codeplex.com/, By the way, It’s a WSP file, you have to add, deploy, and then activate the feature.