Here's a small list for you to check out:
1. Need-Supply: This is one slick e-store. They have a fairly particular style, but even if it's not your cup of tea, they seem to only carry quality goods. Good news is that for every two items they carry that are fairly expensive, they carry one that is reasonable in price (for example, Filson & Carhartt vs Herschel).
I would take a good look at their accessories section as well. I've bought a thing or two from there, and have never been disappointed.
2. J.Crew in Good Company: As a company, J.Crew is hit or miss. I feel like two and a half years ago, they had their heyday, but today, they're potentially on a downswing. Either way, one part of their website that is rarely miss is a part called J.Crew in Good Company. This is their collaboration section, wherein J.Crew curates high quality pieces from other brands, while maintaining their excellent sensibility in style.
Some of my favorite brands like Alden, Barbour, Red Wing, and Drake's are represented in this section, and I have to say... J.Crew is one excellent curator. Unfortunately these items are generally not eligible for sale, but there's always a small subsection that seem to go on clearance. Sometimes you can find a pretty great grab if you browse at the right time.
3. Of a Kind: This site I'm not quite as familiar with, but recently I've been checking up on it quite a bit. I could be wrong, but I believe this site was originally made to help women discover emerging fashion designers. As it turns out, the staff at Of a Kind have pretty good taste, even in the menswear world.
They sell only a small number of items on their site, but I'm a fan of almost all of them. Seems like they have limited quantities of everything too, which makes each item that much more special.