This is probably tougher now than it has been for a few years as the likes of Ponting and Tendulkar slide away and a new generation try to stake their claims. As such, there are surprisingly few nailed on selections for me - no opener really stands out, and once you go past Amla and Clarke you could probably perm from about six or seven names for the remaining middle order slots (Kallis being on the down slope now). Keeper is a comparative embarrassment of riches, with the pure glovework of Jayawardene competing against the classic counter attack of Prior and the conservative options of Sangakkara and De Villiers who are both primarily batsmen. As for the bowlers, Steyn is a nailed on certainty but then any combination of Philander, Anderson, Morkel, Harris, Siddle, Roach, Boult and Broad would have some arguable merit, whilst the debate between Swann and Ajmal is one that could easily fill a whole night in the pub.
My side, for what its worth, is based on the principle that I want to attack rather than sit on the back foot or pack the side with all rounders:
GC Smith
AN Cook (though I seriously considered a left field selection of Chris Rogers as I think his technique has been worked over less)
HM Amla
KP Pietersen
MJ Clarke
AB De Villiers (wkt)
VD Philander
GC Swann or T Boult depending on conditions
DW Steyn
JM Anderson
Saeed Ajmal