Here's some of the best informational sites I've found:
http://www.jetsongreen.com/
http://www.inhabitat.com/
http://www.prefabcosm.com/
http://www.prefabs.com
And here's the list:
http://www.reclaimedspace.com/
http://www.cleverhomes.net/
http://www.bluhomes.com/
http://www.modernistmodularhomes.com/ (below)
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http://www.claytonihouse.com
http://www.clearspacehomes.com/
http://www.formandforest.com/
http://www.mkd-arc.com/
http://www.weehouse.com (below)
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http://www.icgreen.net/
http://www.greenmodernkits.com/
http://www.modesthouse.us/
http://www.jenesysbuildings.ca
http://www.marmolradzinerprefab.com (below)
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http://www.methodhomes.net
http://www.m3house.com/
http://www.microcompacthome.com/
http://numendevelopment.com/
http://www.metroshed.com/ (below)
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http://www.mfarchitect.com/
http://www.modern-shed.com/
http://www.modulardwellings.com/
http://www.mamodular.com/
http://www.moderncabana.com/ (below)
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http://www.placearchitects.com/
http://www.zamorehomes.com/
http://sander-architects.com/hybrid.html
http://www.studio804.com/
http://www.rocioromero.com/
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http://www.sustain.ca
http://www.tkithouse.com/
https://www.homlifestyle.com
http://www.quik-build.com/
http://www.logicalhomes.com/
http://www.methodprefab.com
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http://www.neoshed.com/
http://www.smallworks.ca/
http://www.backyardbox.net/
http://www.blueskyhomesllc.com/ (below)
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http://www.hivemodular.com
http://www.ecooffsite.com
http://www.modern-modular.com/
http://www.nottoscale.com/
http://www.designmobile.com
http://www.piecehomes.com/
http://www.wieler.com (below)
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http://www.re4a.com/
http://www.royalhomes.com/
http://www.stillwaterdwellings.com/
http://www.flatpakhouse.com/ (below)
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http://www.ecosteel.com/
http://www.greenpoddevelopment.com/
http://www.h-haus.com/
http://www.jerikohouse.com/
http://www.fabcab.com/ (below)
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http://www.kithaus.com/
http://www.livinghomes.net
http://www.m-finity.com/
All of these have available models for sale (I came across a lot of research & development sites that looked amazing, but nothing's ever been built). There's a large variation of what's included & what's not included in the price. Some include everything down to appliances & will come and set everything up for you & will help you with permitting etc. Some will just send you a kit with directions. [BTW, Ikea has been making prefab houses in Europe for a few years now]. The $$$ range is huge too. Modern Cabana & M-finity have tiny spaces for tiny prices. Others like Stillwater Dwellings, Blue Sky Homes & Living Homes are pretty pricey & will mail you a 3000 SF house. Many of these firms offer green & even off-the-grid options (soloar, rain water catchment, grey water systems, etc). I've come across a few zero-energy models, which leads me to ask--why the hell are we not all being asked to put these kinds of systems in our houses? Oh right. Because people get pissed when someone mentions when someone suggests white roofs or recycling. Speaking of, I just found Reclaimed Space which looks amazing--they use all recycled materials from previously demolished homes that would be heading for the dump.
PS. Thanks Labhaus! http://www.labhaus.com/
Here are some others I missed:
http://www.containercity.com
http://www.modtech.com
http://www.ecocottages.com
http://www.hybridseattle.com/
http://www.topsiderhouseplans.com