Current favorite is Scarecrow by Matthew Reilly... ok this is a series and its book 5
Sypnosis:
It is set to be the greatest bounty hunt in history....
FIFTEEN NAMES
There are fifteen targets, the finiest warriors in the world - commandos, spies, terrorists. And they must all be dead by twelve noon today. They price on their heads: almost $20 million each.
ONE HERO
Among the names on the target list, one stands out. An enigmatic marine named Shane Schofield, call sign: SCARECROW.
NO LIMITS
And so Schofield is plunged into a headlong race around the world, pursued by a fearsome collection of international bounty hunters...including the 'Black Knight', a notoriously ruthless hunter who seems intent on eliminating only Schofield.
The race is on and the pace is frantic as Schofield fights for survival, in the process unveiling a vast international conspiracy and the terrible reason why he cannot, under any circumstances, be allowed to live....