Facebook acquired several companies between 2007 and 2011 for a total of $60 million. Some of the larger acquisitions included FriendFeed for $47.5 million in 2009, Chai Labs for $10 million in 2010, and Drop.io for $1 million in 2010. The document lists various startups Facebook acquired during this period and the estimated acquisition prices when available.

1. Facebook acquisistions
Total $60M
Gowalla Dec/11
WhoGlue Nov/11
Strobe Nov/11
Digital Saircase Nov/11
Friend.ly Oct/11
Snaptu Sept/11
Push Pop Press Aug/11
Sofa Jun/11
Beluga Mar/11
Rel8tion Jan/11
Pursuit 2011
Zenbe Nov/10
Drop.io Oct/10 $1
Nextstop Sept/10 $2.5M
Chai Labs Aug/10 $10M
ShareGrove May/10
Divvyshot Apr/10
Octazen Solutiona Feb/10
FriendFeed Aug/09 $47.5M
Parakey Jul/07
(Sources and news from http://www.crunchbase.com/company/facebook)