i found this list of bestselling albums from april 2009, but i dont think is accurate,,,but it's as close as it can get
1. Michael Jackson Thriller 72,400,000 (seems inflated , i think it's more likely 65 mill)
2. Pink Floyd Dark Side Of The Moon 41,800,000
3. Soundtrack Grease 40,400,000
4. Whitney Houston Bodyguard 39,600,000
5. Bee Gees Saturday Night Fever 37,200,000
6. 7Eagles Their Greatest Hits 1971-1975 36,700,000
7. Led Zeppelin IV 35,900,000
8. Shania Twain Come On Over 35,400,000
9. Michael Jackson Bad 33,200,000 (if it sells 4 mill it'll be inside the top 5)
10. Fleetwood Mac Rumours 32,700,000
11. Dire Straits Brother In Arms 32,600,000
12. Alanis Morissette Jagged Little Pill 32,200,000
13. AC/DC Back In Black 32,100,000
14. Bob Marley Legend 31,300,000
15. Beatles One 30,800,000
16. Pink Floyd The Wall 30,700,000
17. Mariah Carey Music Box 30,300,000
18. Celine Dion Let's Talk About Love 30,300,000
19. Celine Dion Falling Into You 30,200,000
20. Michael Jackson Dangerous 30,000,000 [/B (could be easily inside the top 15 right now)
21. Guns N' Roses Appetite For Destruction 29,800,000
22. Eagles Hotel California 29,200,000
23. Soundtrack Dirty Dancing 29,000,000
24. Bruce Springsteen Born In The USA 28,900,000
25. ABBA Gold 28,800,000
26. Meat Loaf Bat Out Of Hell 28,700,000
27. Simon & Garfunkel Greatest Hits 28,600,000
28. U2 The Joshua Tree 28,300,000
29. Whitney Houston Whitney Houston 27,900,000
30. Queen Greatest Hits 27,600,000
31. Soundtrack Titanic 27,300,000
32. Beatles Abbey Road 26,400,000
33. Madonna The Immaculate Collection 26,300,000
34. Beatles Sgt. Pepper's Lonely Hearts Club Band 26,200,000
35. Santana Supernatural 26,100,000
36. Backstreet Boys Millenium 25,900,000
37. Metallica Metallica 25,600,000
38. Mariah Carey Daydream 24,900,000
39. Beatles 1962-1966 24,600,000
40. Beatles 1967-1970 24,600,000
41. Nirvana Nevermind 24,600,000
42. Whitney Houston Whitney 24,300,000
43. Eric Clapton Unplugged 24,300,000
44. Phil Collins No Jacket Required 24,000,000
45. Britney Spears Baby One More Time 23,800,000
46. Spice Girls Spice 23,800,000
47. Elton John Elton John's Greatest Hits 23,200,000
48. Bon Jovi Slippery When Wet 23,200,000
49. Madonna True Blue 22,700,000
50. Backstreet Boys Backstreet Boys 22,600,000
51. Queen Greatest Hits II 22,300,000
52. Norah Jones Come Away With Me 22,300,000
53. Phil Collins But Seriously 22,200,000
54. Simon & Garfunkel Bridge Over Trouble Water 22,100,000
55. Boston Boston 21,800,000
56. Eminem The Marshall Mathers LP 21,800,000
57. Celine Dion All The Way… A Decade Of Song 21,700,000
59. Lionel Richie Can't Slow Down 21,600,000
60. Madonna Like A Virgin 21,400,000
61. Prince Purple Rain 21,400,000
62. Pink Floyd Wish You Were Here 21,300,000
63. Ace Of Base The Sign/Happy Nation 21,000,000
64. Britney Spears Oops! I Did It Again 20,800,000
65. Tracy Chapman Tracy Chapman 20,400,000
66. Led Zeppelin II 20,200,000
67. Bon Jovi Cross Road 20,200,000
68. Eminem The Eminem Show 20,100,000
69. Carole King Tapestry 19,700,000
70. Soundtrack Top Gun 19,600,000
71. Michael Jackson History 19,600,000 (it should be 20 mill,even more)
72. George Michael Faith 19,200,000
73. Beatles White Album 19,100,000
74. Def Leppard Hysteria 19,100,000
75. Michael Jackson Off The Wall 19,000,000 (it seems low it stand around 20 mill)