doc_z - 7:29 am on Sep 1, 2011 (gmt 0)
I had the same problem and I'm using the canonical tag. It took some until Google fixed it, but for me it seems to be the best way.
You can also use "noindex,follow", but not "noindex,follow" and the canonical tag at the same time.
I wouldn't use robots.txt to block URLs because it's a waste of link power.