The 30 biggest airports (if you count the amount of passengers) in 2006 were:

1. Hartsfield-Jackson International Airport (ATL) Atlanta, USA - 84 846 639
2. Chicago O’Hare International Airport (ORD) USA - 77 028 134
3. London Heathrow (LHR) England - 67 530 197
4. Tokyo International Airport (HND) Japan - 65 810 672
5. Los Angeles International Airport (LAX) - LA, USA - 61 041 066
6. Dallas-Fort Worth International Airport (DFW) - USA - 60 226 138
7. Paris Charles de Gaulle Airport (CDG) - France - 56 849 567
8. Frankfurt International Airport (FRA) - Germany - 52 810 683
9. Beijing Capital International Airport (PEK) - Beijing, China - 48 654 770
10. Denver International Airport (DEN) - USA - 47 325 016

11. McCarran International Airport (LAS) - Las Vegas, USA - 46 193 329
12. Amsterdam Schiphol Airport (AMS) - Holland - 46 065 719
13. Madrid Barajas Airport (MAD) - Spain - 45 501 168
14. Hong Kong International Airport (HKG) - China - 43 857 908
15. John F. Kennedy International Airport (JFK) - New York, USA - 43 762 282
16. Suvarnabhumi Airport (BKK) - Bangkok, Thailand - 42 799 532
17. George Bush Intercontinental Airport (IAH) - Houston, USA - 42 550 432
18. Phoenix Sky Harbor International Airport (PHX) - USA - 41 436 737
19. Newark Liberty International Airport (EWR) - New Yersey/New York, USA - 36 724 167
20. Detroit Metropolitan Wayne County Airport (DTW) - USA - 35 972 673

21. Minneapolis-Saint Paul International Airport (MSP) - Minnesota, USA - 35 612 133
22. Changi Airport (SIN) - Singapore - 35 033 083
23. Tokyo Narita (NRT) - Japan - 34 975 225
24. Orlando International Airport (MCO) - USA - 34 640 451
25. London Gatwick Airport (LGW) - England - 34 172 492
26. San Francisco International Airport (SFO) - USA - 33 574 807
27. Miami International Airport (MIA) - USA - 32 533 974
28. Philadelphia International Airport (PHL) - USA - 31 768 272
29. Toronto Pearson International Airport (YYZ) - Canada - 30 972 577
30. Munich International Airport (MUC) - Germany - 30 757 978

If you only look at international passengers, the results were:

1. London Heathrow (LHR) England - 61 348 340
2. Paris Charles de Gaulle Airport (CDG) - France - 51 888 936
3. Amsterdam Schiphol Airport (AMS) - Holland - 45 940 939
4. Frankfurt International Airport (FRA) - Germany - 45 697 176
5. Hong Kong International Airport (HKG) - China - 43 274 765
6. Tokyo Narita (NRT) - Japan - 33 860 094
7. Changi Airport (SIN) - Singapore 33 368 099
8. London Gatwick Airport (LGW) - England - 30 016 837
9. Suvarnabhumi Airport (BKK) - Bangkok, Thailand - 29 587 773
10. Dubai International Airport (DXB) United Arab Emirates 27 925 522