WorldClim is a set of global climate layers (climate grids) with a spatial resolution of a square kilometer. They can be used for mapping and spatial modeling in a GIS or other computer programs. If you are not familiar with such programs, you can tryDIVA-GIS.
The database is documented in this article: Hijmans, R.J., S.E. Cameron, J.L. Parra, P.G. Jones and A. Jarvis, 2005. Very high resolution interpolated climate surfaces for global land areas. International Journal of Climatology 25: 1965-1978.
The WorldClim database is under continuous development, please provide us with feedback if you find any problems. The current version is Version 1.4 (release 3). It is only marginally different from version 1.3.
You can download climate data for: