I really like Tasty Vapor. Atomic Cinnacide is a must-try, Geoff's Blend is very nice, and if you like(d) clove cigarettes, their "Kretek" is amazing.
Great liquid and great service, but the best thing of all is their "Doublers". Took me a while to figure it out, but now it's simple. Here's the deal: for every one of their nicotine juices that they sell for $15.30/ounce, there's a corresponding "Doubler", which is zero nicotine juice of the same flavor, for about 1/4 the cost; a 2 oz. Doubler is $10.75, and 4 oz. is $16.25.
You can get the nicotine juice and Doublers in any combination of PG/VG, and you can get the 1 oz. nicotine juice in either 12, 24, 36, or 48 mg. strengths, all the same price. Therefore, it makes the most sense to get the 48 mg. nicotine juice and adjust the level with the cheaper Doublers.
I don't know if other vendors do this, but if they don't, they should. The other obvious advantage of the flavored Doublers is that when you reduce the nicotine level, you're not reducing the flavor, since the Doublers are the same flavor as the nicotine juice.
Some of the other vendors I keep hearing mentioned are Backwoods, V4L, Blumist, Gourmetvapor, VaporTalk, Alien Vision, Vapor Shop, EC Blend, Tasty Vapor, Copper Creek, Mom and Pop's, and Kalamazoo Vapor Shop.