Originally posted by Silvia Renn (WorldFish):

An Inventory and Comparison of  Globally Consistent Geospatial Databases and Libraries
by Joseph F. Dooley Jr., published by FAO in 2005, 

...is a great compendium of commercial and public domain geodata. Part II is especially interesting as it lists, compares and assesses available geodata.

http://www.fao.org/docrep/008/a0118e/a0118e00.HTM

"The inventory is divided into two parts: with Part One of the inventory presenting overview, terminology and summary sections of globally consistent data libraries; while Part Two contains a categorization of the data sources identified broken into topical subsections based on the individual core data layers specified by UNGIWG and FAO. The report also includes a matrix rating the suitability of the various data sources identified to each of the core data layers specified by UGIWIG and FAO, and introduces Virtual Base Maps as a potential cost-effective means for: providing spatial referencing to remote field offices, enhancing Internet map serving capabilities, and facilitating mapping via GPS handheld devices."