LandScan is the finest resolution global population distribution data available and represents an ambient population (average over 24 hours) at 1km resolution (30"x30"). Annual datasets for the years 2000 through 2011 can be accessed via a web map or downloaded in their entirety.
More information is available on the Library's LandScan database information page.
Contact Jon Jablonski for more information. jonjab [at] library [dot] ucsb [dot] edu or (805) 893-4049.