I don't think anyone in the world can beat the collection that the Sultan of Brunei had:
http://www.automotoportal.com/article/Sultan_of_Brunei_His_private_automotive_empire
5000 cars
..and as if a collection of 5000 cars isn't amazing by itself, but most of these cars are some of the rarest in the world.
Here is the list of cars:
http://www.deluxeblog.it/post/1984/lelenco-delle-auto-del-sultano-del-brunei
HON NSX BN2328 JHMNA12800T400079
HON NSX BN2200 NA1000374
HON NSX KE9933 NA11001229
HON NSX BN7999 JHMNA12600T001135
HON NSX BN7799 JHMNA12800T400054
HON NSX KE9595 NA11001303
HON NSX BN2000 JHMNA12600T300007
HON NSX KF9087 JHMNA12600T000563
HON NSX BN7272 JHMNA12800T400124
HON NSX BL9336 JHMNA12600T000759
HON NSX BM2218 JHMNA12600T100111
HON NSX BM7272 JHMNA12600T100021
HON NSX BP1888 SHMNS12800T4000089
HON NSX BL8809 JHMNA12600T0010335
HON NSX KE9078 SHMNA11000824
HON NSX BN138 JHMNA12800T400123
HON NSX BP2189 JHMNA17800T400077
HON NSX KE9955 NA11000291
HON NSX BN7227 JHMNA12800T400110
HON NSX BM7891 JHMNA12600T001028