Here's a fun one.  A site collection was created on a development portal to test database restores.  When the database backup was restored to the portal, SharePoint lost all access to the site collection.  The site collection was still listed, but no information returned about the database, and of course no access to the portal URL.  As SharePoint couldn't access the database, it was deleted from SQL.  Easy enough, but how do we get rid of the site collection?

I found a good post at TechNet, which basically says to do the following:

• Open SQL Server Management Studio
• Expand SharePoint configuration database
• Expand Tables
• Locate 'dbo.SiteMap', right click on it and select "Edit Top 200 Rows"
• Find the row containing the site you want to delete
• Right click on the row and select "Delete"

Also, don't forget to remove the content database from SharePoint Central Administration!