It's called Structural Insulated Panels, or SIPs. They work really well for garages, my next door neighbor built his out of SIPs a couple years ago. Construction is really fast, and they have excellent thermal and sound insulation. The material costs are generally higher than standard studwall construction, but because they go together so fast you save money on labor and the end cost is pretty comparable.
Do a google search on 'SIPs' and you'll find a lot of information, here one good link:
http://www.toolbase.org/techinv/techDetails.aspx?technologyID=114