WSO2 ESB comes with a mediation statistics component, which allows users to collect and monitor statistics on proxy services, sequences and endpoints. Data gathered by this component can be viewed through the ESB management console or one can even develop some custom code to pump the data into an external monitoring tool.
I just published an article titled "WSO2 ESB Mediation Statistics: What Can Numbers Tell About Your SOA?" which explains the ins and outs of the mediation statistics component along with how to process the collected statistical information by writing custom code. Enjoy!