Hokay, I'll have a go - the following list starts after the Great War only because that allows for the chance of at least some archive footage.
Bradman, Sutcliffe, Hutton, Hammond, Tendulkar, Lara, Richards, Sobers, Ponting, Miandad, Compton, Worrall, Steve Waugh, Clive Lloyd, Border
Its not an easy task because there are so many variables - I initially included George Headley but then discounted him on grounds of his relatively brief test career - harsh, but then what would one do with Barry Richards and Graeme Pollock who would surely merit places on this list if they had had a bit longer?
Idon't personally place too much store in the weight of runs scored by modern players - they get more games to score them in - nor do I look purely at averages because the conditions are so obviously variable. I've ignored players currently at or close to their peak because, well, we just don't know where they will eventually get to - though Kallis, who is past his peak, is left out on purpose because he is, when it comes down to it, a fat blocker with one eye on his average! Likewise, no Geoff Boycott...
Some of you may perceive a couple of these to be odd choices - if you want me to elaborate I'm happy to...