i've seen a couple of solutions and so far the Automation container (Belgium) seems to be the most versatile one. Standard there are 8 versions but many more are possible.. what i really liked was the fact that you don't need to move the racks to get to the rear and the fact that it's completely autonomous! Generator/fire/access/UPS are included. I even saw a model which displayed a container village, a power and chiller platform and several data containers depending on the customer load.
I think for modular data center following approach is must:
• A place to locate computer, storage, and networking devices safely and securely.
• To provide the power needed to maintain these devices.
• To provide a temperature-controlled environment within the parameters needed to run these devices.
• To provide connectivity to other devices both inside and outside the data center.