Creative and technically adept cabinetmakers used to be the norm, and they still exist, albeit in small numbers compared the the number of new homes being built every year. Unfortunately, we see this craft becoming more and more the sole purview of kitchen design firms and very high-end contractors who specialize only in kitchen and bath work. Most homes are not made by the same sorts of craftspeople who built our old bungalows; they're assembled from pieces made in factories all over the world. There are, however, a number of fine woodworkers specializing in casework and other forms of built-in furniture for all parts of the home and various other types of interior architecture working across the North America today, and I've spent a little bit of time reading up on a few who have their work up on the web to peruse.
This list is, of course, very incomplete and totally subjective; please feel free to append other listings in the comments, below.
There are a number of decent enough books on designing, planning and building your own built-ins (including the Tolpin book, reviewed here on HH). Those of us who are not experienced woodworkers, however, will need to hire someone who actually knows what they are doing.
Connecticut-based Viking Kitchen Cabinets are highly recommended, and despite their name specialize in built-ins of all types.
Dana Robes Wood Craftsman, in Enfield, New Hampshire, take custom furniture commissions in addition to carrying a stock of Shaker-inspired items for sale. They specialize, however, in interior architecture and cabinetry of all types. They also offer a schedule of week-long and weekend workshops [update 09.07: Dana Robes Wood Craftsman closed in September 2006].
Jason and Angela Frantz of WoodShop Artisans are cabinet- and furnituremakers who specialize in Murphy beds. Their site also offers a short documentary photo-journal of a current kitchen project in process.
NePalo Cabinetmakers are located in Northern Marin County, over the Golden Gate bridge from San Francisco, and have hand-crafted a range of furniture items and built-ins in the Arts & Crafts style, like these beautiful - and immense - mahogany wall units.
Ashwood Woodworking & Furniture is located in Sebec Corners, Maine, in the heart of the Maine Highlands. Their large shop is located in a historic 1840s barn. While their focus is on kitchens (and sometimes custom homes), they've completed a number of other built-in projects, including various Craftsman cabinetry jobs and a number of pieces of custom furniture, principally tables.
Wallen Woodworking, like its sister firm Carlson Custom Cabinets, is located in the Minneapolis / St. Paul area. The vast majority of their work is the finishing & casework of custom kitchens and the ever-popular fireplace surrounds and entertainment centers in homes built or altered by parent company Knudsen / Wallen / Peterson / Hauer Construction Services.
Neil Kelly cabinets in Portland Oregon has a number of Craftsman- and Shaker-influenced designs in their quasi-custom repertoire. I say quasi, as it appears that much (but certainly not all) of their work uses at least some premade components).
Walt Stanley of Brookside Woodworking in Castleton, Vermont is primary a furniture builder but also has done some custom kitchen work, in the same beautiful Vermont maple and maple burl veneers that he uses for so much of his work.
Gary Bulla's Architectural Woodworks, located in Santa Paula, California, specializes primarily in cabinetry, furniture, custom kitchens and doors. Bulla is especially interested in the Arts & Crafts movement and the majority of his commercial work has been in this style.
Certainly the big commercial shops, most of whom create their "custom" work from customer-supplied measurements far away from the actual installation site, have also put together good-looking kitchens, bathrooms and other sorts of built-in projects.
Crown Point Cabinetry, a family-owned company located in is Claremont, New Hampshire, straddles the line between the small local craftsperson and the nation-wide "custom" cabinet provider. I've only seen a few examples of their work, and it seems superior to the sort of thing you could find through Home Depot or Lowe's or your generic big-box home improvement / hardware store.
There's always something not quite right about work put together without regard to the room, house, and character of the owners themselves - things that a local and experienced craftsperson will take into account when building for you. Make your cabinetmaker part of the design process - don't just go to them with finished drawings. A good cabinetmaker has the experience to know not just what works well, but what looks best.