The dev kit shown below is very recent, anonymous sources told us it was produced on August 18th 2005.


3 Xbox360 Dev Kits next to each other, controller, headset and a SmartXX LT OPX
 
On the leftside image you see a Toshiba-Samsung TS-H943 DVD-ROM and in the background the aircooled heatsinks of CPU (left) and GPU (right) (the final retail Xbox360 is expected to be watercooled according to the ourcolony movie). The right image shows the the southbridge made by SiS.

 
On the left you see the top of the motherboard with both the heatsink of GPU and CPU removed: you can see the IBM PowerPC CPU on top and the ATI Xenos GPU (with its EDRAM) below. On the right of the GPU you can see 2 Samsung memory chips. The right picture shows the bottom of the motherboard    
From left to right:
(1) The (proprietary?) power connector, clear change from the connector of the current Xbox - let's hope Microsoft won't have to recall these. On these Dev Kits the AC adapter is external, the final retail will probably have it internally.
(2) Special outputs on the Dev Kits (won't be on retail units)
(3) Chip with a "VER 1839.2" sticker on. Could this be a kernel/firmware/bios version?
(4) There's a 2nd smaller PCB inside the Xbox 360, I think (if I see correctly) it's placed on the front, just behind the power button (ring of light). It also handles the wireless controllers.

Many more pictures are available showing specific parts of the XeDK motherboard and also the dvd-rom, cables, controller, memcard, headset, plugs, ports ... you can download the whole set of pictures on smartxx.com website, smartxx.com forums.