It looks like if you want I/O options you need to buy a Mac mini. Ethernet, FW800, HDMI, Thunderbolt, 4x USB3, SDXC, Audio in & out, infrared.
The specs for the iMac say of the audio jack, "Support for Apple iPhone headset with microphone". So there is audio in hiding in the port.
The two Thunderbolt ports certainly have potential, but I don't think we've seen external boxes with a variety of I/O ports in them.
The SD slot location looks like a huge...