If you're looking for agencies who have it down I'd recommend Ogilvy Social W+K Social and RGA. But it really depends on how you want to position your agency, you'll see they all take pretty different approaches.
Before looking at other examples I'd recommend figuring out who exactly you aim to be or who your customers want you to be and go from there. There are hundreds of ways to do social and the only definition of right or wrong that counts comes from your clients.
Take a look out the ones I manage:
Let me know if you want to chat about how I maange them or if you have specific questions.