http://en.wikipedia.org/wiki/List_of_languages_by_number_of_native_speakers

Language    Family    Native speakers
(Ethnologue 16)[1]    Total speakers
(Ethnologue 16)[1]    Other estimates    Rank
Mandarin    Sino-Tibetan,
Chinese    845 million (2000)     1025 million    One of the six official languages of the United Nations.
All varieties of Chinese: 1,200 million (2000)    1
Spanish
(Castilian)    Indo-European,
Romance    329 million (1986–2000)     390 million    400 million native.[2] 500 million total (2009)[3]
One of the six official languages of the United Nations.
2
English    Indo-European,
Germanic    328 million (2000–2006)     —    Approximately 375 million L1 speakers, 375 million L2 speakers, and 750 million EFL speakers. Totaling about 1.5 billion speakers.[4]
One of the six official languages of the United Nations.
3
Hindi-Urdu
(Hindustani)    Indo-European,
Indic    240 million (1991–1997)     405 million (1999)    490 million total speakers.[5]    4–5
Arabic    Afro-Asiatic,
Semitic    206 million (1999), 221 million, 232 million
(206M is "all Arabic varieties"; 221M is Arabic "macrolanguage", not counting Hassaniya; 232M is sum of counts for all dialects)     452 million (1999)    280 million native.[6]
One of the six official languages of the United Nations.
4–5
Bengali
(Bangla)    Indo-European,
Indic    181 million (1997–2001)     250 million        6–7
Portuguese    Indo-European,
Romance    178 million (1998)     193 million    220 million native, 240 million total.[7]
Ethnologue estimate misses ~12 million in Angola[citation needed]
6–7
Russian    Indo-European,
Slavic    144 million (2002)     250 million    One of the six official languages of the United Nations.[8]    8
Japanese    Japonic    122 million (1985)     123 million        9
Punjabi    Indo-European,
Indic    109 million (2000)
All varieties: Lahnda, Seraiki, Hindko, Mirpur     —        10