Here's a running list of DIY build it yourself Gasifier plans findable online.  If you know of others, please add to list.

GEK / Gasifier Experimenter's Kit, ALL Power Labs
http://gekgasifier.pbworks.com/How-to-Build-and-Run-the-GEK-Gasifier

Fluidyne (Doug Williams)
http://www.fluidynenz.250x.com

LaRosafier Double Rotor (Mike LaRosa)
http://tech.groups.yahoo.com/group/WoodGas/messages?o=1

Mother Earth News / MEN Gasifier
http://www.motherearthnews.com/Green-Transportation/1981-09-01/Wood-Gas-Update.aspx

FAO 72: Wood Gas as Engine Fuel

ISBN92-5-02436-7, UN Food and Agricultural Organization, 1986 

http://www.allpowerlabs.org/gasification/resources/papers/FAO72.pdf

Handbook of Biomass Downdraft Gasification

Thomas Reed and Agua Das, SERI/SP-271-3022, DE88001135, March 1988. 

http://www.allpowerlabs.org/gasification/resources/papers/Handbook.Reed.Das.pdf"

(available in print from BEF at http://woodgas.com/bookstore.htm. please support BEF. the entire BEF library is fabulous. buy the whole thing.)

Wood Gas for Mobile Applications (Vesa Mikkonen)
http://www.ekomobiili.fi/Tekstit/Bookbrochure.pdf

FEMA Manual- Constructing a Simplified Wood Gas Generator for Fueling Internal Combustion Engines in a Petroleum Emergency
Henry LaFontaine, F.P. Zimmerman, March 1989
http://www.allpowerlabs.org/gasification/resources/papers/FEMAsimplifiedGasifier.pdf
(available in print from http://woodgas.com/bookstore.htm  please support BEF. the entire BEF library is fabulous. buy the whole thing)
Also on the Gengas.nu site at http://www.gengas.nu/byggbes/index.shtml

Markus Almroth Gengasiddan site in Sweden (translated via Google)
http://translate.google.com/translate?hl=en&sl=sv&tl=en&u=http%3A%2F%2Fwww.gengas.nu%2F

Dutch John micro-gasifier plans
http://www.woodgas.nl/microgasifiers/microgasifiers.html
 
Stig-Erik WERNERS
http://www.gengas.se/build_gasifier.htm

Windward Gasifier (Walt Patrick)
http://www.windward.org/notes/notes63/wal63_b.htm

Design Rules for Downdraft Gasifiers: a short review, Jan Venselaar
http://wiki.gekgasifier.com/w/file/34997261/DesignRulesforGasifiers-JanVenselaar.pdf

Sizing charts for Imbert and Stratified Downdraft Designs
http://www.allpowerlabs.org/gasification/resources/index.html

Complete list of resources, books, articles and data is over in the GEK

http://wiki.gekgasifier.com/w/page/6123742/General-Resouces#view=page