As you all know, Ribbon customization has got a great significance in CRM 2013 as well.
I would like to recommend the following Ribbon Customization tool. Please note that I haven't tried all scenarios but got good outcomes for the customization that I tried with this tool.
It provides a good overview of the Ribbon structure in CRM 2013. In my opinion its a nice tool.
The installation and short demo could be found in the below link. Also you could find the Ribbon Workbench download links.
Ribbon workbench by Scott Durow -- "http://www.develop1.net/public/page/Ribbon-Workbench-for-Dynamics-CRM-2011.aspx"
( Ref: http://www.develop1.net/public/page/Ribbon-Workbench-for-Dynamics-CRM-2011.aspx)