Question: Where can I find a good Eclipse Mercurial Plugin?

Answer: 
Vectrace is dead. They say you need to go to javaforge ( <http://cbes.javaforge.com/update> ).  
WARNING: plugin on javaforge is unsigned and cannot be verified.
Here is the web-site: <http://www.vectrace.com/mercurialeclipse/>  

The update site is: <http://www.vectrace.com/eclipse-update/>