List of subways (and other train-like mass transit systems) I've ridden on.

• Chicago: “El”, Metra
• New York City area: MTA, NJ Transit, PATH, LIRR
• Tokyo: Tokyo metro
• Washington, DC: Metrorail
• Dublin: Luas
• Paris: Metro
• London: Underground
• San Francisco: BART
• Boston: “T”
• Philadelphia: SEPTA

Rapid Transit Systems in the US, by ridership (via wikipedia)

1. NYC Subway
2. Metrorail (Washington, D.C.)
3. Chicago 'L'
4. “T” (Boston)
5. BART (SF Bay Area)
6. SEPTA (Philadelphia)
7. PATH (New York / New Jersey)
8. MARTA (Atlanta)
9. Metro Rail (L.A.)
10. Metrorail (Miami)
11. Baltimore Metro Subway
12. PATCO (Philadelphia)
13. RTA Rapid Transit (Cleveland)
14. Staten Island Railway
15. Detroit People Mover

http://en.wikipedia.org/wiki/List_of_rapid_transit_systems http://en.wikipedia.org/wiki/List_of_United_States_commuter_rail_systems_by_ridership