Fully white label? As in... an API you can use? In which case, Disqus. Or just comments on things? In which case, Disqus. Also, if you're doing forums as Sa

Fully white label? As in... an API you can use? In which case, Disqus. Or just comments on things? In which case, Disqus. Also, if you're doing forums as SaaS you really need to think about the kind of anti-spam, moderation and admin tools that you're going to provide. I don't know if you've ever seen the admin section of vBulletin, but there's a reason why vBulletin is so widely used and it's not to do with the front-end.