Quite simply Kallis is in the same league as Lara, Tendulkar and Ponting and anyone who thinks otherwise is deluded.
Of course he's a lot more boring than the 3 mentioned above. As a purist I enjoy watching Kallis almost unshakeable technique, but of course Lara, Tendulkar and Ponting were far entertaining. This does not put them in a different league, it only makes them more watchable. Kallis may score a 100 and Lara may score a 100 in the same circumstances, Lara's will be far more entertaining and memorable, but in terms of what they offer the team it's pretty much the same. Yes Lara might be faster but it's test cricket, there are 5 days and sometimes it can be good to take time out of the game. So Kallis might be less of a matchwinner and more of a match saver, but I don't see why Lara turning a draw into a potential win is any better than Kallis turning a loss into a potential draw.
I would have Lara and Tendulkar ahead of him but not by much, and Ponting due to his recent slump (yes it is that close) on a level with him. Dravid would be maybe very slightly less than those 2. But the point is it's all very close.
As for those who don't think Kallis is a matchwinner, just because we dont see him scoring dramatic 4th innings hundreds doesnt mean he isnt. I havent bothered to check, but I have seen plenty of matches where Kallis has set up a match by scoring a first innings hundred.
As an overall test player he is easily the best of the last 20 years, and I'm not a South African or Kallis fanboy. I just get frustrated with his lack of hype, not neccesarily so much on these boards but among the general public.