Hi,
I think the industry standard would be our/Go2Group's JaM plugin. You can see the product here, as well as a partial list of our JaM customers at the bottom of this page: http://www.go2group.com/en/products/go2group-jam-plugin/, it supports defects, test cases and requirement replication and two directional syncs.
JaM costs $3,000 for unlimited users.
We offer free evaluations and remote installation consulting via our ticket system and also by live web meetings from our engineering staff.
We also have a new integration platform, ConnectALL, which can integrate many to many ALM tools, including JIRA and Quality Center (as well as DOORS, TFS, ClearQuest etc). For more information, see http://www.go2group.com/en/products/go2group-connectall/