By 2012 the following London tube stations will be accessible (Source: Mayor of London):
1. Barking (Zone 4, currently step-free)
2. Bermondsey (Zone 2, currently step-free)
3. Brixton (Zone 2, currently step-free)
4. Caledonian Road (Zone 2, currently step-free)
5. Canada Water
6. Canary Wharf (Zone 2, currently step-free)
7. Canning Town (Zone 3, currently step-free)
8. Chalfont & Latimer, (Zone C, currently step-free)
9. Chesham (Zone D, currently step-free)
10. Chorleywood (Zone B, currently step-free)
11. Dagenham Heathway (Zone 5, currently step-free)
12. Earls Court (Zone 1/2, currently step-free)
13. East Ham (Zone 3/4, currently step-free)
14. Elm Park (Zone 6, currently step-free)
15. Epping (Zone 6, currently step-free)
16. Fulham Broadway (Zone 2, currently step-free)
17. Hammersmith (District) (Zone 2, currently step-free)
18. Hammersmith (H&C) (Zone 2, currently step-free)
19. Harrow & Wealdstone (Zone 5, currently step-free)
20. Heathrow T123 (Zone 6, currently step-free)
21. Heathrow T4 (Zone 6, currently step-free)
22. Hillingdon (Zone 6, currently step-free)
23. Hounslow East (Zone 4, currently step-free)
24. Hounslow West (Zone 5, currently step-free)
25. Kensington Olympia (Zone 2, currently step-free)
26. Kew Gardens (Zone 3/4, currently step-free)
27. Kilburn (Zone 2, currently step-free)
28. London Bridge (Zone 1, currently step-free)
29. New Cross (Zone 2, currently step-free)
30. North Greenwich (Zone 2/3, currently step-free)
31. Richmond (Zone 4, currently step-free)
32. Southwark (Zone 1, currently step-free)
33. Stanmore (Zone 5, currently step-free)
34. Stratford (Zone 3, currently step-free)
35. Sudbury Town (Zone 4, currently step-free)
36. Tottenham Hale (Zone 3, currently step-free)
37. Upminster (Zone 6, currently step-free)
38. Upney (Zone 4, currently step-free)
39. Uxbridge (Zone 6, currently step-free)
40. West Finchley (Zone 4, currently step-free)
41. West Ham (Zone 3, currently step-free)
42. Westminster (Zone 1, currently step-free)
43. Willesden Junction (Zone 3, currently step-free)
44. Wimbledon (Zone 3, currently step-free)
45. Woodford (Zone 4, currently step-free)
46. Woodside Park (Zone 4, currently step-free)
47. Wembley Park (Zone 4, currently step-free)
48. Acton Town (Zone 3)
49. Archway (Zone 2/3)
50. Clapham South (Zone 2/3)
51. East Putney (Zone 2/3)
52. Edgware (Zone 5)
53. Euston Square (Zone 1)
54. Finchley Central (Zone 4)
55. Finsbury Park (Zone 2)
56. Golders Green (Zone 3)
57. Greenford (Zone 4)
58. Green Park (Zone 1)
59. Hainault (Zone 4)
60. Harrow-on-the-Hill (Zone 5)
61. Heathrow T5 (New Station)
62. Hendon Central (Zone 3/4)
63. High Barnet (Zone 5)
64. Highbury and Islington (Zone 2)
65. King’s Cross St. Pancras (Zone 1)
66. Ladbroke Grove (Zone 2)
67. Leytonstone (Zone 3/4)
68. Mile End (Zone 2)
69. Morden (Zone 4)
70. Newbury Park (Zone 4)
71. North Acton (Zone 2/3)
72. Oakwood (Zone 5)
73. Paddington (Zone 1)
74. Pinner (Zone 5)
75. Rayners Lane (Zone 5)
76. Roding Valley (Zone 4)
77. Shepherd’s Bush (Central line, Zone 2)
78. Southfields (Zone 3)
79. Stockwell (Zone 2)
80. Tooting Broadway (Zone 3)
81. Tottenham Court Road (Zone 1)
82. Tower Hill (Zone 1)
83. Vauxhall (Zone 1/2)
84. Waterloo (Zone 1, Jubilee Line currently step-free)
85. Wood Lane (New Station)
Step-free means accessible from plattform to the exit, not from plattform into the train. :-)