The picture shows the disc tray, two memory ports, a power button and a possibly covered extension port. In addition there seems to be an IR port and maybe a button to trigger a wireless connection. Since no connectors are visible for the connectors, it's likely that the Xbox 360 will feature wireless controllers -- as has been suspected by many.
This, probably somewhat older, picture shows the left hand side of the console at an angle. You can see that the color is a bit different, and the eject button is facing a different direction. The bulge you see on the first picture seems to be a HDD expansion slot (note the "40GB" marking).
This picture, which surfaced before the ones shown above, looks a bit different from the others. Either this is a newer design of the HDD expansion or the slot is covered by a "default plate" which is used when no expansion device is installed.
In my opinion the device looks quite nice already!
Sources:
Xbox-scene
Spong