Juicy Vapor has a huge variety of juices and sampler pack configurations, the smallest being 3 3ml bottles. BTW their Butter Rum Caramel is pretty good (as in I dripped a bit and then immediately ordered a bigger bottle).
Velvet Vapors has 5 samples for $12.95 or you can buy samples individually - I recommend the Raspberry Ginger Ale (or plain Ginger Ale if you want)
PureVapes has 0mg samples only
FreedomSmokeUSA has 24mg samples only, and only of some of their many juices and tobaccos. Not sure if they have them in samples but their Cocoa is great for cutting the sweetness of another juice or tobacco. And I love their oRYental 4 (a sweet caramel tobacco I vape and used to sweeten other tobaccos) and their Voodoo is interesting
Madvapes Topvapor juices are as cheap as samples sometimes
I like juices around 70pg/30vg or any high-PG blend. I just bought more juices a minute ago. I picked up Juicy Vapor Chocolate Covered Orange Caramels, Irish Cream Brownies and B52 (tobacco)
(that B52 one made me smile remembering drinking B52's w/ some Canadian guys at a bar in Canada out of tall slim shooter glasses with the layers of liquor. I stole one of the glasses. I do not usually steal stuff but I had never seen glasses like that and we spent a ton in that bar every night and I tipped extra that night. I wrapped it in socks in my luggage. And during the trip Canada customs/security searched my luggage as I stood there. He pulled the shooter glass out of the sock - what is this?" hahahahaha how embarrassing)
