I would throw High Fashion Home in the mix.

http://www.highfashionhome.com

there's always craigslist...

A trip to Ligne Roset is more bitter than sweet. While the furniture is well made and very comfortable & attractive, their pieces are very pricey.

RESTORATION HARDWARE has a beautiful selection of sofas (as well as other furniture), although I cannot attest to their furniture quality.

.....Troy closed a few years ago. How are they still on the list?

Another vote for Flexform as a high end candidate. My wife and I were looking for a minimalist looking but cushy feeling sofa this past year and must has sat in 50 sofas in four countries. We felt like Goldilocks: too hard, too soft, rarely just right. Most of the ones that looked good to us (le.g., the Bensen Neo mentioned above), were too hard to sit in. Flexform has several sofas that passed the cushy test. Also consider Living Divani, another high end Italian sofa - their Family Life and Box sofas also fit our cushy requirements.

Eh...Perhaps stop into the Conran Shop? Not seeing anyone mention that here.

My best find in all these years is my Perobell Sofa from Spain. Incredible. Oberon is the style. Every single person that has layed or sat on this has been in awe with the comfort. It is very deep also.

http://www.designprovision.co.uk/sofas/perobell_sofas.html

What's great you will only see this in design mags not someone elses apt. First rule of design. It all starts with the sofa. Go big there cut corners on storage and wood related products. Meaning ikea does just fine for bookshelves, etc.

I have purchased from an online manufacturer called simplicity sofas. You can see their product here: http://www.simplicitysofas.com

They have apartment size high-quality sofas, not IKEA quality. They also have full size living room furniture too. I buy the groups for my condos. The sets arrive in boxes so you can easily get them up stairs or elevators. I assembled the sofa in 10 minutes!! No tools needed. And the quality is awesome. It is all MADE IN THE USA too! High Point, NC

They specialize in small scale sofas and ready-to-assemble sofas, and offer a choice of 50 different fabrics as well as optional slip covers. You can give them your own fabric too! Check it out.

I didn't check through all the many comments already posted but I have to mention this website...if you live on the East Coast, its free shipping! http://www.carolinagirlfurniture.com

I would like to offer one store where I got a great sectional sofa. This store isn't so popular and it hasn't got Super luxurious furniture. Most of the sofas are affordable and qualitative enough.

All this raving about the Charles sofa from B&B...As an unfortunate owner of this terrible piece of furniture, I say find something else! It's uncomfortable and it's cushions needs to be plumper up permanently for it to look half decent. Worse still, the cushion cover rotates round the seat cushion, giving the impression that the stuffing is depleted along the front edge. Finally, its pièce de résistance: the chaise longue skids away from the sofa when you sit on it. Don't waste your money. It looks great at the moment of delivery, thereafter, it looks and feels like a whore's mattress.

I can't believe Shabby Chic hasn't been mentioned! All their pieces are custom made in the US, and they're the most comfortable, practical slipcovered pieces sofas you'll ever have. Probably in the higher end price range, but definitely worth it. Been loving mine since 2004! I know they closed down for a little bit of time, but I think they've reopened on Mercer Street in Soho.

I would add Zin Home Sofas to that list. High End Sofas and Sectionals with more affordable prices.
http://www.zinhome.com/simena-sectional-sofa/
http://www.zinhome.com/florence-style-loft-sofa/
http://www.zinhome.com/simena-sofa/