Top 30 Cities by Metro System Ridership

From: http://en.wikipedia.org/wiki/Metro_systems_by_annual_passenger_rides

1. Tokyo (Tokyo Metro, 2270 mil.; Yamanote Line, 1345 mil.; Toei Subway 832 mil.) total 4447 mil.
2. Beijing, 3209 million
3. Seoul, 2560 million
4. Shanghai, 2500 million
5. Moscow, 2491 million
6. Guangzhou, 1990 million
7. New York, 1655 million.
8. Mexico City, 1609 million
9. Hong Kong, 1600 million
10. Paris, 1541 million
11. London, 1229 million
12. Shenzhen, 914 million
13. Berlin (U-Bahn 507 million; S-Bahn 395 million) total 902 million.
14. São Paulo, 877 million
15. Singapore, 854 million
16. Osaka, 842 million
17. Cairo, 837 million
18. St. Petersburg, 772 million
19. Santiago, Chile, 649 million
20. Taipei, Taiwan, 635 million
21. Delhi, 606 million
22. Prague, Czech Republic, 589 million
23. Tehran, Iran, 568 million
24. Vienna, Austria 568 million
25. Madrid, Spain 558 million
26. Kiev, Ukraine 536 million
27. Caracas, Venezuela, 485 million
28. Nanjing, 452 million
29. Barcelona, Spain 449 million.
30. Nagoya, Japan, 443 million
31. Milan, Italy 426 million
32. Athens, Greece 407 million
33. Manila, Philippines (LTR and MRT), 405 million
34. Rio de Janeiro, 402 million

I included more than 30 because the bottom 5 have similar numbers.