Pre-PoD:
1. United States
2. Soviet Union
3. United Kingdom
4. France
5. PRC
Post-PoD (1960s):
6. Australia (defense against Communist Indonesia, Commonwealth assistance)
7. Canada (tactical use by RCN and RCAF)
8. Israel (historical reasons)
Post-PoD (1970s):
9. Sweden (maintenance of neutrality and independent nuclear shield)
10. Switzerland (maintenance of neutrality and independent nuclear shield)
11. Yugoslavia (defense against Soviet Union, help from NATO)
12. Nationalist Spain (Franco wanted a Spanish nuclear program)
13. Albania (defense against Soviet Union, help/purchased from PRC)
14. India (defense against PRC, Soviet help)
15. Pakistan (defense against India, Commonwealth/United States help)
16. Communist Indonesia (Australia has them, help from PRC and/or Soviet Union)
17. Argentina (historically strong nuclear program, nuclear weapons legitimized)
18. Brazil (defense against Argentina)
19. Chile (defense against Argentina and Brazil)
20. South Africa (historical reasons)
Post-PoD (1980s, massive breakout):
21. West Germany (NATO pressure)
22. Italy (NATO pressure)
23. Greece (rivalry with Turkey)
24. Nationalist Portugal (nationalism)
25. Democratic People's Republic of Korea (historical reasons)
26. Republic of China (defense against PRC and others)
27. Japan (earlier remilitarization, defense against everyone else, even the DPRK has a bomb)
28. Burma (defense against others and independent nuclear shield)
29. Malaysia (defense against everyone else)
30. Singapore (defense against everyone else, unable to field a large army)
31. Imperial Iran (seems like something the Shah would do)
32. Turkey (Israel and Iran have them)
33. Egypt (Israel has them, Arab bomb)
34. Saudi Arabia (defense against Israel and Iran, rivalry with Egypt)
35. Iraq (defense against everyone else)
36. Syria (defense against everyone else, rivalry with Iraq)
37. Algeria (Maghreb bomb)
38. Libya (Gaddafi or the King wants it, unable to field a large army)
Post-PoD (1990s, massive breakout):
39. Vietnam (defense against everyone else, help from Soviet Union)
40. Philippines (defense against everyone else, help from the United States)
41. Colombia (everyone else is doing it)
42. Venezuela (everyone else is doing it)
43. Jordan (defense against everyone else)
44. United Arab Emirates (defense against everyone else, unable to field large army)
45. Kuwait (defense against everyone else, unable to field large army)
46. Nigeria (African bomb)
47. Angola (rivalry with Nigeria)