This plugin adds a rel=”nofollow” tag when linking to external sources. All domains on the list will be rel nofollowed.
It’s based on the Wikipedia nofollow plugin and now allows you to add/remove/edit domains from a blacklist.
Note: If you add for example wikipedia.org every subdomain from wikipedia will be rel nofollowed, but if you add en.wikipedia.org then only the subdomain will be rel nofollowed.

Is it possible to rel=no follow ALL links on all posts?
1Terrible. It is pitty.
2