As far as Masters are concerned:
(tie) 1. Nadal: 21 - Indian Wells (2), Monte Carlo (*8*), Hamburg (1), Madrid (1), Rome (6), Canada (2), & Shanghai (1)
(tie) 1. Federer: 21 - Indian Wells (4), Miami (2), Hamburg (4), Madrid (2), Canada (2), Cincinnati (5), Shanghai (1), & Paris (1)
3. Agassi: 17 - Indian Wells (1), Miami (6), Rome (1), Canada (3), Cincinnati (3), Madrid (1), Paris (2)
4. Djokovic: 13 - Indian Wells (2), Miami (3), Rome (2), Madrid (1), Canada (3), Shanghai (1), Paris (1)
Djokovic now joins Federer as the only player to have won 7 of the 9 Masters. Each has won them all, except:
Djokovic: Monte Carlo & Cincinnati
Federer: Monte Carlo & Rome
Additionally, they are the only two who have made the finals of each event.