I've just been looking through the supplier's forum myself, trying to find the best price on a 510 starter kit. Here's a list of US suppliers currently offering the best prices on 510 kits and gear:
(I've ordered from the Widow twice before, and highly recommend her - rock bottom prices and fast, free shipping. Considering Vapor Station this time since they're running a special on new custom colors, and their kits come with 3 batteries, 2 manual and 1 auto).
Widow's Bead Work
Vapor Station
Good Prophets
City Smoker
E Cig Supply
My Vapor Store
The Smoke Safe
Diet Smokes
Vapor Guys
Cig Techs
E Cig Express
Electro-Nic-Stix
(Sorry, can't post URLs yet, but most of these vendors are on the supplier's forum if you do a search...)