Sorry for the clueless question, but does coinbase act as an exchange? If so, at which volume compared to the others?
Coinbase is more like a paypal for bitcoin for US customers. You can see a real time price ticker at:http://btcquote.com, but not sure how much order book info is open to the public.
edit: there is also a simple chart of transacitons per day here:https://coinbase.com/charts. Its unclear if it is coinbase volume though.