Official download site for Taverna workbench is no longer SourceForge, but:
http://www.taverna.org.uk/download/
Also see new official download mirrors:
https://launchpad.net/taverna/t1
https://launchpad.net/taverna/t2
http://code.google.com/p/taverna/downloads/list
Older versions of Taverna are still available here for archival reasons.