Here are few high PR Site for SEO.
- http://www.techsupportforum.com/ (PR 5)
- http://forums.searchenginewatch.com/ (PR 6)
- http://www.flickr.com/help/forum/en-us/ (PR 9)
- http://forums.adobe.com/index.jspa (PR 9)
- http://www.v7n.com/forums (PR 5)
- http://acapella.harmony-central.com/ (PR 4)
- http://answers.yahoo.com (PR 8)
- http://forums.digitalpoint.com/ (PR 4)
- http://www.dmoz.org (PR 8)