Here's some high-res world population density data, based on a 2.5' grid wherever possible. Data is from the great people at the Gridded Population of the World project:
Gridded Population of the World (GPW), Version 3.0 (v3) beta
Citation Information:
Originator: Center for International Earth Science Information Network (CIESIN), Centro Internacional de Agricultura Tropical (CIAT).
Publication Date: 2004
Title: Gridded Population of the World (GPW), Version 3.0 (v3) beta
Geospatial Data Presentation Form: raster digital data
Publication Information:
Publication Place: Palisades, NY
Publisher: CIESIN, Columbia University
Online Linkage:
http://beta.sedac.ciesin.columbia.edu/gpw/