It’s really hard to answer a question like this, because photography is such a personal hobby in so many respects. Some people prefer all the modern electronic gizmos on their cameras (multi-point autofocus systems, multiple light-metering options, motordrives, auto flash bracketing, etc., etc.), while others are happy to stick with fully manual cameras such as the legendary Nikon FM2. If money is no option, then one of the top-of-the-range Nikon or Canon autofocus pro cameras (Nikon F5 or Canon Eos-1V), or maybe even a Contax, which takes the magnificent Carl Zeiss lenses. But these and other manufacturers also make cheaper cameras that do just about everything the serious amateur needs. And, as people in the photography chat-rooms that i read constantly point out, it is the person behind the viewfinder that really makes the photo.
I have a Minolta 35mm AF system, with Maxxum 8000i and 9xi bodies, two zoom lenses (35-80mm and 100-300mm) and six prime lenses (24/2.8, 28/2.8, 50/1.7, Tamron 90/2.5 Macro, 135/2.8, and 200/2.8 Apo). I’ve been very happy with it, although lack of time and a certain amount of apathy mean that i’m contemplating trading it in for a good digital 5 megapixel camera, like the Nikon Coolpix 5700 or Minolta Dimage 7hi.
But i digress. I’ve been happy with the Minolta kit, but if i were starting again i would probably go for a system that has a larger choice of new and second-hand lenses. Minolta has generally been considered (a bit unfairly, in my view) not to be quite as “serious” as Nikon and Canon, with the result that fewer pros and high-level amateurs use the system. This translates to fewer second-hand Minolta AF lenses coming onto the market, and Minolta doesn’t have as good a range of new lenses as Canon and Nikon. Nowadays, with the rise of competent lens-only manufacturers like Sigma, Tamron, and Tokina, this is not such a problem. These manufacturers make AF lenses for all the big name camera brands, and in some cases their optical quality is approaching that of the camera manufacturers themselves.
Still, if i were starting again, i would probably be choosing between a Nikon and a Canon system. The great thing about a Nikon system is that Nikon’s lens mount has remained essentially unchanged since the days of manual focus-only cameras, which means that older manual focus lenses will fit on new autofocus bodies, and vice-versa, albeit with some loss of metering and autofocus function. This leaves you with a huge variety of second-hand lenses to choose from. Many Nikon users also love being able to carry an old FM2 body with them, in case heat or cold or lack of batteries leave them unable to shoot. The FM2 is a completely manual camera that will run without any batteries in almost any temperature conditions. No other sytem that i know of offers you such versatility.
What features you want on your camera will also depend on what you intend to shoot. For someone like me who likes taking landscapes, a depth-of-field preview function is essential. It’s also nice to have lenses that have d-o-f markers on the barrel. If you’re an action person, you will probably want a fast autofocus system, as well as lenses with good, wide manual focus rings for when you want to do it yourself. Most high-end SLRs have a fast motordrive option, but i’ve never had occasion to use the 4.5 frames-per-second function on my camera.
You will also face the choice of whether to go for zoom lenses or prime (single focal length) lenses. If you’re going to be shooting at a lot of business meetings and conferences, as you suggest in your OP, you probably don’t want to be carrying around a whole bunch of lenses, so i would recommend a good zoom lens that goes from a moderate wide angle to a medium telephoto, something like a 35-105, or even one of the new 28-200mm lenses if you want the flexibility of a 7x zoom. OTOH, you also want to do some landscapes and some portraits, which means you’ll need wide angle capability, as well as medium-long, wide aperture telephoto.
In your position, and if i had the money, i would probably opt for three zoom lenses - a 20-35/f3.5-4.5, a 28-105/f3.5-4.5, and a 70-200/f2.8. This would give you very wide angle through to telephoto coverage. The fast (and expensive) f2.8 telephoto zoom would give you a nice wide aperture for portraits and for any action shots you wanted to take. If you had money to burn, you could also opt to make the other two lenses f2.8 also, but i really don’t think it’s necessary, especially for the wide-angle zoom.
A dedicated flash would, of course, be necessary for your indoor shots at conferences etc. You could go with the manufacturer’s model, or a third-party type such as Metz. If you really wanted to take serious studio portraits, rather than just available-light shots, you might also want to invest in some studio lighting equipment, but i don’t know anything about that stuff. And, for the landscapes, a tripod and cable shutter release are essential.