Since there are now two major world bodies - the professional World Darts Council and the amateur World Darts Federation - it's a difficult question to answer.
For the WDF, the major determining tournament is the Embassy World Professional which is held in early January each year. It's name originates from a time when there were no divisions between amateur and professional. Since it belonged the British Darts Organization, the tournament is now essentially an amateur event with World Darts Council members and other pros banned from participation by the World Darts Federation. The 1996 Embassy champion was Steve Beaton (England).
The WDC, on the other hand, have several major annual tournaments. Players acquire points depending on how they place in each tournament. Consequently, player ranking is effected by, not only how well a player may do, but how often he plays. The top positions are fiercely contested by the major players and the number one player this month may be number three next. At the time of writing WDC Pro Rankings Top Five standings dated May 27, 1996 are:
1 Phil Taylor England
2 Dennis Priestley England
3 Alan Warriner England
4 Jamie Harvey Scotland
5 John Lowe England