I somehow missed this thread the first time around, but I'll post what works for me. For the record, my dimensions are:
6'3" 175 lbs. (due to lifting weights and eating 4 meals a day [or 3 meals plus protein shake]. I'm down from my max of 185 lbs. because I'm not working out enough, but still better than my high school physique, many years ago, when I was 6'3" and 135 lbs.).
Rather than writing about specific brands, I'll share my general guidelines:
(1) Fit is critical for people with a "custom" physique, so a good alterations tailor is most important. I'm making mine rich, since I now get almost everything I buy OTR tailored, including jeans. Shirts get taken in on the sides, armholes raised, and arms slimmed. Trousers usually get the waist and seat taken in and always get cuffed, unless there's not enough fabric (no cuffing on jeans though). I usually widen trousers below the knee. I don't want clothes clinging to my thin body and accentuating my slender build. 90% of my trousers are flat-front, but I will wear single pleats if they fit my waist and seat (it's really a good look and can add a little heft).
(2) Horizontal details are my friend. This means I wear plaids, checks, horizontal stripes, and extra pockets (ticket pockets on jackets and suits, two chest pockets on shirts), epaulets on shirts, and shirt sleeves rolled up near the elbow. Until very recently I wouldn't wear vertical stripes, but I get away with them on top, since I have very long legs and a striped shirt elongates my torso. Beware plaid or checked suits, though. Most are made with longer vertical than horizontal lines to make the average hefty Joe look taller and thinner...not something I need.
(3) Heavy and/or textured fabrics are good--flannels, linens, cavalry twill, tweeds, corduroy (wide-wale or waffle corduroy, no thin-wale cords) and denim.
(4) Layer whenever possible. Double-breasted jackets are great (I have a charcoal gray, double-breasted peacoat from Sterling that I love) and layering a sweater under a jacket adds visual weight. Cable-knit sweaters add bulk; crew necks minimize vertical lines and/or a long neck (I avoid most v-necks for this reason). I recently started wearing a knit vest and got multiple compliments. Vests are a great way for me to layer since they present no issues with sleeve length (and can add layers in summer, at least in some climates).
(5) Use color to break up vertical lines. I wear contrasting colors on top and bottom, a slightly wider belt than usual to break myself in half visually, and contrasting socks. The rule to match sock and trouser color is designed to elongate the leg line, not something I need, so I break the rule often.
If you can afford it, I recommend finding a good tailor and having a few basic pieces such as a navy blazer and a charcoal gray suit custom made. I have a custom blazer that fits like a dream and I wear it all the time.
My remaining challenges are finding a leather jacket and casual, button-up shirts. I now get my business shirts MTM, but can't find interesting fabrics for casual shirts. Nor can I find a tailor who will work with leather
To summarize: Know your own body, know the rules of fit, color, and pattern, know when to follow the rules and know when to break them to get the look you want. There are certainly times when I want to celebrate my tall, slender physique and I know how to do that, too (For example, I really enjoy wearing my tuxedo in midnight navy with vertical shadow stripes [double-breasted, with peak lapels]).