Quon Modular is a semi-custom prefab system from Australia. Each room is a (mostly) self-contained module, measuring 5 m x 3.1 m (16 ft x 10 ft). Buy exactly what you need placed side-by-side, stacked, or each by itself.
Materialicio.us loves the concept:
"For me, this is the simplest, most efficient system yet devised for a customized, prefabricated house. Design your house using their standard components, place the order, and ten weeks later it's delivered."
Few prefabs offer such a flexible approach. The weeHouse series from Alchemy Architects allows for the addition of specialized modules, such as the sleepTight, but their modules vary in size. v2world was offering a similar product in their v2shell, but last we heard, they were reworking their product line.
company: Quon Modular
size: each module is ~140 sf
price: starts at ~$150,000 for 4 modules (br, bath, kitchen, multi-purpose)
finish level: complete, inside and out, including light fixtures, utilities, and finish
(More coverage: Treehugger)
Exchange rate used: $A1.168 = US$1.00