Here's my hit list:
Www.keh.com - always some good finds, and always a wide range of stock. They under-rate everything so even a "bargain" is a bargain!
Www.tamarkin.com - Dan Tamarkin is a really great guy, I almost bought from him once and he was so incredibly helpful and interested in conversing over the product. He made sure I felt I was getting top notch service. He's got great deals on his site too.
firstname.lastname@example.org - Ken Hansen used to have a store in new York, but deals from pretty much any location now. He is very fair, and prompt, and you can always trust him.
email@example.com - Youxin Ye is a Leica repairman, self taught too, but he is an amazing guy. He fixes up old Leicas and sells them for a really good deal, and since he has worked on it himself, you have that assurance of proper function. If anything ever goes wrong, he's got the best deals in town (town being the USA). Send him your Leica for a CLA at least once a year!