DIY Supplier List

These are a list of online suppliers where you can safely purchase your DIY materials or other vaping items.  I've only listed the ones that I have personally ordered from with little to no trouble.

DIY Supplies

Capella (to order CAP flavorings directly from the manufacturer)
Ecig Express (PG, VG, liquid nicotine, tobacco absolute, and flavorings by FA, FW, LA, LAN, FE, NF, SF, Jungle, Hangsen, Tasty Puff, INA, CAP, and NW)
E-Liquid Mart (PG, VG, liquid nicotine, and flavorings by FA and CAP)
The Flavor's Apprentice (to order directly from the manufacturer)
Vaping Zone (PG, VG, liquid nicotine, and flavorings by VZ and Hangsen)
Wizard Labs (nicotine, pg, vg, and flavorings by TFA, LA, LAN, CAP, Seedman and Wizard Labs)

Premade Liquid Companies

Backwoods Brew
Halo
Mt. Baker Vapor
My Freedom Smokes
Revolver
Totally Wicked
Virgin Vapor

Honorable Mentions

Provape (Home of the ProVari)

DIY Shorthand

If you visit any of the vaping forums found online and look up recipes for liquids, then you'll often find a bunch of letters.  I will unlock the mystery of the letters for you:
CAP:  Capella - the name of a flavoring manufacturer most famous for their Vanilla Custard version 1 or 2.
DIY:  Do It Yourself - A term used to denote a group of people in the vaping community who enjoy mixing their own liquids.
DV:  Decadent Vapours - this is a UK based flavoring and e-liquid company.  They also offer premixed complex flavorings that only require the need to add a nicotine solution of nicotine, pg, and vg to the mix.
ECX:  Ecig Express - they also make a line of flavorings using TFA/TPA bases.
FA:  Flavourart - an Italian based flavoring manufacturer.  They make concentrated flavorings to be used at low percentages.  I have read that they were the first or perhaps the only flavoring manufacturer to test their flavorings specifically in vape liquids whereas others manufacturer their flavorings for use in foods.
FE:  Flavor Express/Fruit Express - a line of flavorings made by ECX.
FW:  Flavor West
HS:  Hangsen
INA/INW:  Inawera - a Swedish based (I think) flavoring company
JF:  Jungle Flavorz
LA:  LorAnn - a flavoring company most famous for making candy flavorings.
LAN:  LorAnn Naturals - this is a specific line of organic flavorings produced by LorAnn.
MOL:  Molinberry flavorings
NF:  Nature's Flavors flavorings
NW:  Northwest Flavors (new flavoring line found at ECX using a VG base)
PG:  Propylene Glycol - the carrier fluid in vape liquid.
SM:  Seedman flavorings
TA:  Tobacco Absolute - a highly concentrated tobacco extract that requires being diluted first before adding to liquids.
TE:  Tobacco Express - a line of flavorings made by ECX.
TFA:  The Flavors Apprentice; also known as The Perfumer's Apprentice (TPA).  Mostly veteran vaping enthusiasts know it by the latter name.
TP:  Tasty Puff (not to be confused with toilet paper - sorry some vape humor there).
TW:  Totally Wicked - a vaping supplier that carries both devices and liquids.  Link found above.
VG:  Vegetable Glycerin - a thick liquid found in most vape liquid.  It has a sweetness to it and is found in higher levels in liquid designed for sub-ohm vaping at higher temperatures.
VZ/VZSC:  Vaping Zone/Vaping Zone Super Concentrated - they sell flavorings without PG for those with PG sensitivities.

The above list of acronyms are ones that I have collected over the years, but there is a more comprehensive list found here.  It also contains some lesser known acronyms that I, personally, have never used.

*Note

E-Liquid Mart offers free shipping on orders over $50.00.  Vaping Zone offers free shipping on orders over $75.00

I am currently working with Flavourart flavorings in my own DIY adventures so I'll usually order from Ecig Express, or Eliquid Mart when placing orders exclusively for flavors.  If I'm looking for lab equipment; measuring tools, funnels or safety gear; then Wizard Labs is my "go to" place.  I've  tried nicotine liquid by all of the manufacturers above and have not had a problem with any of them.  I usually order a 50/50 nicotine mix.