RMD Aircraft Lighting, Inc (http://www.rmdaircraft.com)
An outstanding company I've encountered is RMD Aircraft Lighting, Inc. They have been more than helpful to me and most communication was via email. I asked for a larger than normal RV wingtip lens and they were able to accommodate me by sending their normal lens before trimming. Time will tell if it works for me. My plan is to use a headlight reflector from a late model (probably a 2004 Honda Accord) car in the wingtip. There will be several advantages. It is easily replaceable should it be damaged. It has remarkable reflectivity. I can have both HID landing lights and halogen recognition lights. Plus, the intensity of the strobe will be increased as will the LED position lights. The drawback is that most, if not all, car headlights are made of one unit - the reflector and plastic lens are all one piece. So, the reflector will have to be cut away and then fitted to the wingtip. Still, should look very nice and provide great lighting. RMD makes an excellent wingtip light for RVs.
Blue Mountain Avionics (www.bluemountainavionics.com)
Greg Richter of BMA has been very receptive from my first meeting with him. He allowed me to pay for my EFIS yet delay delivery until needed. That has worked out great. I've received my EFIS Lite and both magnetometers, but postponed delivery of the EFIS One. That is exactly the service I needed because I don't have storage room for the additional parts. Greg and company are receptive to suggestions and frequently implement the suggestions. They constantly work on upgrading their products.
Boelube
I wish I had known about Boelube when I started building. I bought the paste and use it on screws that will be in nutplates and on drill bits to make easier and cleaner cuts.
Perihelion Design (http://www.periheliondesign.com)
Few technology suppliers match the quality and service of Perihelion Design (http://www.periheliondesign.com). I ordered Eric's Powerschottky and Wig-Wag module and found his service to be prompt and courteous. He has been very helpful with numerous questions about electrical issues. The products I've seen thus far from Perihelion Design are of the highest quality. I recommend http://www.periheliondesign.com to you.
Advanced Flight Systems (www.advanced-flight-systems.com)
I've bought the AOA Sport from AFS (actually the company they bought it from) and I plan to buy their AF-2500 Engine Monitor. I am impressed with the capabilities of the AF-2500 and the resolution of the display. Most impressive, though, is the responsiveness of the company owner. Every time I've called, I've actually had a human answer the phone (didn't have to choose between American or spanish) and they are always pleasant, patient, and informative. I recommend them.
Microfasteners (www.microfasteners.com)
Rivethead Aero - Rivethead
Here is a cool canopy handle that the maker will engrave for you.

Plane Power Alternators ( www.plane-power.com)
Plane Power of Granbury, TX produces an internally regulated 60 Amp alternator. You can visit their web site at www.plane-power.com.
Ariel Trim Mixer (http://www.arielate.com/?categoryId=505)
Tools