The Summer Institute for Linguistics (SIL) Ethnologue Survey (1999) lists the following as the top languages by population:
(number of native speakers in parentheses)

1. Chinese* (937,132,000)
2. Spanish (332,000,000)
3. English (322,000,000)
4. Bengali (189,000,000)
5. Hindi/Urdu (182,000,000)
6. Arabic* (174,950,000)
7. Portuguese (170,000,000)
8. Russian (170,000,000)
9. Japanese (125,000,000)
10. German (98,000,000)
11. French* (79,572,000)

[Source]