Landthieves is the best that I've seen but even it's not great...not well moderated with a lot of profanity, opinions aren't supported with facts, just a bunch of juvenile banter. The Kahlil McKenzie thread was hysterical..but it's the best they've got.
The Rivals/247 sites aren't very good for any discussion. There's other sites that are geared towards the older fans but aren't very active Soonerfans/Soonertimes