With a little bit of modding, I have managed to fit my undersize mATX motherboard (24.4cm x 19.4cm) into a Lian Li mITX case: the PC-Q07.
I had to cut a new motherboard tray from a removable motherboard tray I bought online, as well as cut out some of the rear of the case to accommodate the changed position of the I/O area. This also required swapping the left and right panels, as the mITX motherboard mounts are built into the right panel.
I've used some modder's mesh to turn the DVD bay into an intake vent, and covered the ATX PSU holder with modders mesh as well.
While I was taking my PC apart, I took the opportunity to swap the stock NB cooler for a Thermalright HR-05 IFX and the stock SB cooler for a Zalman ZM-NB47J.
I've moved my Samsung F1 1Tb into an external hard drive cage as well.
Intel E5200 @ 2.2Ghz and 1.0V
Thermalright HR-01 Plus with Scythe Slipstream 800rpm @ 5V
Gigabyte G31M-ES2L (mATX)
2 Gb stick of Kingston HyperX DDR2-800 RAM at default timings
PW-200V with 60W brick (largest I could find with no active fan)
OCZ Vertex 60Gb SSD (OS drive)
1 Tb Samsung F1 HDD (in ASTONE external HDD cage)
Again, you'll have to forgive the poor quality photos from the camera on my mobile phone.
(You can see the external HDD cage sitting between the case and the speakers on top of some open cell foam, which reduces the vibrational noise a little bit when the HDD is on, along with the DVD bay vent which is the main intake for the CPU fan, the sole fan in this build).
(Not much to see really, the vent at the top also functions as a bit of an intake area for the CPU fan. This used to be the right panel, but I had to swap them as explained above.)
(You can see the silver of the motherboard tray through the now-useless ventilation holes from what used to be the left panel.)
(You can see the hole I had to cut to fit the I/O board. The modders mesh coving the PSU area looks pretty good IMO.)
(Pretty minimal clutter inside, given the hardware I am using. The clearance between the HR-01 on the CPU and the HR-05 on the NB is pretty slim.)
Oh, and for anyone who is wondering, the speakers the PC is setting next to are a set of Logitech Z-10 2.0 USB speakers.
Next on the agenda is swapping to a picoPSU 150W XT and a 12.5A brick, as the PW-200V covers most of the SATA ports (even though I'm not using them). I also want to play with a little overclocking and the current 60W brick won't allow enough headroom.