Take this with a grain of salt, since I'm still a TRUE vaping newb, but...
If you haven't already, check out Mt. Baker Vapor. They have tons of flavors, and their juices are insanely cheap. You can order 5 15ml juice bottles for what you'd pay for a sampler pack just about anywhere else, and you get to pick all five of the flavors (which is not always the case with samplers). Plus, they add in a freebie anytime you spend over $15 before shipping and after discounts. And shipping, even first class, is super fast.
They even have coupons for 10% off your order (ECF is one, and vaporfrombaker is another). No clue if they're reusable.
The downside is - all their juices are made to order, and a LOT of their flavors benefit from a week or two of steeping. If you're not feeling really patient, you may end up disappointed with some of their flavors - especially the more complex ones - right out of the mail. I'm still hoarding a bottle of maple pecan because I'm worried it hasn't bloomed fully yet. Going to try to give it a second full week before I load that one up.