I' m kind of a toss up between a couple sets of three.

My first instinct would be basically a military set up, with one alteration:
.22-250 (in place of the 5.56Nato)
.308Win (or .300Winmag)
12.3x97mm(.50bmg)

However, my current set up does well I believe:
.22-250
.30-06
.416Rigby

Breaks my heart no to have a .44mag in there, or a .45-70gov., so I' d have to have my wife buy three guns for me to borrow: .44mag, .45-70 and a 7.62x39mm just for fun