Even the 4th contender in the way of the Sony Alpha range. They took over the Minolta line, and a few Nikons and all of the new Pentaxes use Sony Sensors
I can't comment on the alpha 77 or the full frame alpha 99, but the A700 comes out trumps for me
It's worth bearing in mind that Nikon and Canon do *not* feature in-body image stabilization and require a specific IS lens, whereas Sony and Pentax can use any compatible lens and have stabilization applied at no extra cost
Having worked with Nikons at my last job and dealing with them through my new company I have to mention that Nikon's aftersales support is far better than Canon, they offer free sensor cleaning, lens cleaning for the lifetime of the camera
The Canon images are always more saturated than the Nikon images, that's something worth bearing in mind if you do go for a Canon
As for what body to buy, I'd advise either a D7000 with a grip (I cannot work without a grip, just personal preference) or a D300s without a grip (the bodies are expensive enough without a grip. Rather spend the money bo batteries). If you're feeling adventurous you can try the second hand market at Kameraz in Rosebank, look for a D200, D300, D300s, or if money allows a full frame second hand D700 or D3
Canon: go for either a 5D, 5D mk 2 or a 7D, bear in mind that if you went for the 5D you would have to purchase an external flash unit
Would I buy a D600 or 6D? If you're a pro then I would avoid it like the plague. Limited features, and a very limited shutter speed of 1/4000th of a second