BDC Catalog Designer from Microsoft!
Microsoft have released a tool for developing BDC XML catalogs (applications) and it’s part of the Microsoft Office SharePoint Server August SDK.
Update: 28 November 2008 – Warning; this tool cannot do SQL Server 2005/2008 schemas. This means you cannot use it against AdventureWorks, but you can use it against AdventureWorksDW. This is an astounding limitation given Microsoft’s push towards using schemas. If you try, you’ll get the error “Could not process Table ‘….’. Make sure you have SELECT Rights on the Table/VIEW”. This needs to be fixed.