gvSIG Open Source GIS softwaer

At http://www.gvsig.gva.es you can find more info (also in English, if you click the right flag).
gvSIG is a tool oriented to manage geographic information. It is characterized by a user-friendly interface, with a quick access to the most usual raster and vector formats. In the same view it includes local as well as remote data through a WMS or WFS source.

Available as both binaries and source-code, for Windows, Linux and OSX.