http://www.aircraftspruce.com/cathome.php  Aircraft Spruce and Specialty -- good source for just about everything related to homebuilt aircraft.  Their catalog also has a lot of very useful reference information and guidance on how to do things.

http://www.wicksaircraft.com/  Wicks Aircraft -- the other large homebuilder supply house.  Some prefer Wicks customer service to Aircraft Spruce, but I've had good experience with both.

http://www.avmapnavigation.com/  AvMap Satellite Navigation -- A wide range of GPS navigation devices.  I plan to install the AvMap EKP IV, which can be mounted in either portrait of landscape orientation, has pretty much all the features of the high-end Garmin hand-held units at less than half the cost, and with a signifcantly larger display.

http://www.dynondevelopment.com/  Dynon Development -- Glass cockpit flight instrument display, engine monitor, and combination in one package.  This is the one I am leaning toward for my Sinus.

http://bluemountainavionics.com/  Blue Mountain Avionics -- Led the way in affordable glass cockpit technology for homebuilt aircraft.  They have sold a bunch, offer a range of products and prices, and seem to have a decent reputation.  My observation is that the display is a bit jerky, seemingly caused by trying to extract too may operating features from a single processor.  My real hesitance with the Blue Mountain units is that Greg Richter, a very brilliant engineer, designed everything, and is the only one who really understands the product (in my opinion).  If you buy a Blue Mountain, you are buying Greg, and if he decides to go away and do something else, there is no backup.  Greg has been doing a great job, and provides an amazingly responsive level of technical support while continuing to expand and improve the product line, but I'm wary of the one-man-band nature of the operation.

http://www.controlvision.com/  Anywhere Map -- A wide range of PDA-based moving map displays, software and related products.

http://www.advanced-control-systems.com/  Advanced Flight Systems -- combined flight instrument and engine monitor glass cockpit display.

http://hometown.aol.com/enginfosys/  Grand Rapids Technologies -- engine monitor and separate flight instrument glass cockpit display.

http://www.i-ktechnologies.com/  I-K Technologies -- line of engine monitors.

http://www.lockwood-aviation.com/las.php Lockwood Aviation Supply -- Phil Lockwood is the Rotax engine guru in the USA, and offers a comprehensive range of parts and accessories.  He also runs a licensed Rotax repair station and provides very informative Rotax engine forums at most of the major homebuilt aircraft fly-ins in the US.  Last summer he announced that he was offering Rotax engine operator courses at his facility in Florida, which I had planned to attend, but now I don't see them mentioned on his web site.

http://www.aeroelectric.com/  The Aeroelectric Connection -- This is a must for understanding, designing and building the electrical system for your aircraft.  Bob Nuckolls, the owner of Aeroelectric, knows this area better than anyone else I've found, and you really should read his book.  I also highly recommend that you join his e-mail discussion group, which you can do by clicking the Aeroelectric List link at the bottom left corner of his home page.  If you glance through the e-mail traffic daily, most of your questions will be answered in time, and Bob does an amazing job of answering questions that are directed to him.  The discussion group alone will provide you an excellent free education on all things practical in the realm of light aircraft electrical systems.

http://www.asa2fly.com/ Aviation Supplies and Academics (ASA)  -- They carry all the basic reference books, plus a large range of instructional materials and software.

http://www.soarmn.com/cumulus/index.htm  Cumulus Soaring -- This looks like an excellent source of information, equipment and avionics related to soaring.  A very useful feature is the product comparisons section of the site.  For instance, http://www.soarmn.com/cumulus/varios.htm provides a very comprehensive and useful comparison of just about every available variometer on the market.

http://www.trutrakflightsystems.com/index.html  True Trak Flight Systems -- A relatively new, but well-received vendor of autopilots, aimed specifically at the homebuilt market.

http://www.trioavionics.com/index.htm  Trio Avionics -- Another homebuilt aircraft autopilot that emerged from the canard community.  I like their products, and I hear nothing but complimentary comments on their products.

http://navaid-devices.com/ Navaid Devices -- Also provides an autopilot product.  It's not as commonly installed as the other two above, but those who have one seem happy with it.  Doesn't have any fancy features, but the price is also lower than the others.

http://www.mcmaster.com/ McMaster-Carr -- A great resource for all kinds of things.  Hand and power tools, shop equipment, fittings, etc. etc.  They have stuff that you will find extremely helpful.  The real challenge is that they offer so much that you don't even know what to look for.

http://www.kitlog.com/ KitLog Pro -- Provides a very nice software package to maintain your builder's log.  Tracks your build activity, expenses, vendors, etc.  Also includes a handy library of FAA advisory circulars and pertinent regulations.

I strongly encourage membership in at least one national organization.  Whether or not you agree with everything these groups do, they are increasingly important as advocates of private and recreational flying.  Restrictions on flying and reductions in personal flying privileges ratchet in only one direction, and the general public just doesn't identify favorably with our pastime. 

"You're building an airplane in your garage?!!!!  Is that legal?  Where are you permitted to fly it?  etc. etc."   Even if you are flying a factory-built airplane, the image is one of extravagent and dangerous activity that they silently (or perhaps not silently) mistrust.  Arguing that they willingly drive down the highway at closing speeds of 120+ mph, passing other three-thousand-pound cars 24 inches away that are driven by people of entirely unknown competence, and contrasting that with the miniscule personal threat posed by a 800 pound aircraft a thousand feet overhead, just doesn't work.

So, lend your support (and get some very useful information and assistance) by joining a group, including a local chapter.

http://www.eaa.org/  The Experimental Aircraft Association (USA).  If you join, select the Sport Pilot option in addition to the basic membership.  The Sport Pilot monthy publication specializes in light aircraft and has regular articles on Rotax engine operation and maintenance.

http://www.pfa.org.uk/index.asp  The Popular Flying Association (United Kingdom)  Membership in PFA is mandatory if you are going to build an aircraft in the UK. 

http://www.aopa.org/  Aircraft Owners and Pilots Association -- by far the largest and most influential pilot organization in the US, with associate organizations in other countries.  The monthly publication, AOPA Pilot, alone makes membership worthwhile.

http://esoaring.com/  The Experimental Soaring Association (formerly the Sailplane Homebuilders Association) -- specifically organized to provide mutual support and information exchange among sailplane homebuilders.

http://www.ssa.org/  Soaring Society of America -- Join this one for sure.  Glider pilots are a very small community, and we really must band together to keep the sport alive and legal.  The public perception is that flying without a motor is even more dangerous to the general population than powered flight.  Membership includes a very nice monthly magazine.

Additional Pipistrel construction photos -- The Pipistrel kit manual is already very complete, and with a little thought and the great support from the factory, you can build the airplane.  Somewhere along the way, however, I was given a CD with about a thousand photos taken during the build documentation process.  I have found those photos to be very helpful in clarifying a number of details as I have started building.  I highly recommend that you ask for this file if you purchase a kit.

FAA Advisory Circular AC 43.13 Acceptable Methods, Techniques and Practices - Aircraft Inspection and Repair -- This is the standard reference that every A&P mechanic learns to use.  It touches on pretty much anything you'll need to do when working on or building an aircraft.  Available from ASA and lots of other places, including the US Government Printing Office.  I've got revision 1A Change 3, but I see that it's up to 1B Change 1 now.