I've tried a few vendors, and have some new orders on the way, but so far, tasty vapor and mr-e-liquids juices are the best i've come across.
Tip: although Tasty Vapor doesn't sell samples of their liquid, you CAN get 6ml TV samples at mr-e-liquids.com. He doesn't have all of their flavors, but he does have a good assortment. Mr. E's juices are just as good as TV's IMO. I just placed an order from DIYflavorshack, based on tons of rave reviews I've seen...the jury is out until I get them, so I'll check back later with that info.
I agree that it's good to start w/ sample sizes, so you don't break the bank and end up w/ big bottles of stuff you hate. One I would avoid though is Johnson Creek. Sorry any JC lovers out there, but I got the sample pack, and they all taste the same to me, and it's not a good taste! But then, like they say, taste is subjective...so its your call.
I'm only a month and 1/2 into this, so there's a lot more exploring to do. Read the reviews, watch the videos, but try to find a reviewer that has similar tastes to you to get a better feel for what you'd like. For example, I'm really into the sweet stuff, so I gravitate to reviewers that like that quality also but there are others who really dig the tobacco flavors, etc.