One of the cool new features introduced in SharePoint 2010 SP1 is the Site Recycle Bin feature.
Earlier, the only way to restore deleted sites and site collections required to restore the appropriate content databases. But from SP1 onwards, deleted sites can be recovered from the Site Recycle Bin.
Deleting and Restoring Sites (SPWeb)
When users delete a site, they are presented with the following page:
Read more here.