They are:
Sachin Tendulkar (35 centuries)
Steve Waugh (32)
Brian Lara (31)
Ricky Ponting (31)
Rahul Dravid (22)
Gary Kirsten (21)
Marvan Atapattu (16)
Adam Gilchrist (16)
Others that are close:
Matthew Hayden needs a century against Bangladesh
Inzamam Ul-Haq needs one against South Africa
Jacques Kallis - Sri Lanka
Justin Langer - Bangladesh and Zimbabwe
Mohammad Yousuf - South Africa and Sri Lanka
Michael Vaughan - New Zealand and Zimbabwe
Stephen Fleming - India and Zimbabwe