The equivalent of the weblogic-ejb-rdbms-jar.xml is map.mapxmi which defines the CMP mapping.
ibm-ejb-jar-bnd.xmi is a binding file which serves the specific purpose of mapping references and to the real JNDI elements and defining JNDI names for EJB, etc... WebSphere gives you the opportunity to override settings in this file at aplication installation time
ibm-ejb-jar.ext.xmi is for any setting that extends the J2EE spec for example defining access intent on an EJB.
You will find detailed info on these files in my book. The link in my signature can take you there.
Roland Barcia: IBM Distinguished Engineer, CTO Mobile for Lab Services