First, and foremost, Don Bradman. No batsman was a bigger match winner. His team won 30 of his 52 tests, with him averaging 130.08 in those matches.
Headley's team didn't win many matches (5 of 22), but he did average 95.75 in those 5 matches.
Sobers - 31 tests won of 93, him averaging 77.42 in them
Sangakkara - 47 won of 117, avg 75.04
Mahela - 53 of 138, avg 62.97
(Twosome effect)
Chappell - 38 won of 87, avg 70.49
Hammond - 29 won of 85, avg 69.83
Hobbs - 28 won of 61, avg 68.00
Sutcliffe - 25 of 54, avg 62.97 (not too different from his mean)
(Twosome effect)
Lara - 32 won of 131, avg 66.76
Hutton - 29 won of 79, avg 65.31
Dravid - 56 won of 164, avg 65.78
Tendulkar - 70 of 198, avg 62.36
Laxman - 47 of 134, avg 55.90
(3 in different combinations)
Graeme Smith - 57 won of 110, avg 60.28
Kallis - 80 of 162, avg 62.57
Sorry for not listing Ponting and Viv here, but I don't think they were the biggest match winners in their respective teams.
I know this isn't the best metric, but it's a starting point.
P.S. The twosome effect may be in place for others as well, I haven't been thorough.