Not many people know this, but if your Cisco router is running a recent (within the last 3 years or so) IOS version, it comes with a built-in, application-layer packet sniffing application called Network Based Application Recognition (NBAR). This utility was originally designed for the world of Quality of Service (QoS), but is now used for many different capabilities. Try this:
On your router, access the interface connected to the Internet and type the command ip nbar protocol-discovery. That will enable your packet-sniffing application. Now, exit back out to privileged mode and type the command show ip nbar protocol-discovery stats bit-rate top-n 10.