A recent Morning Edition story on National Public Radio discussed the efforts of the USDA to collect aerial photographs spanning the nation through the National Agriculture Imagery Program (NAIP). NAIP imagery is taken yearly during the growing season for the purposes of administering USDA programs.
NAIP imagery has been collected in various levels of detail (resolution) and availability over the last couple years. In Wisconsin, 2004 and 2005 NAIP imagery is available as a free download through WisconsinView. The 2005 imagery is state-wide with 1 meter resolution in MrSID compressed image format. The 2004 NAIP has 2 meter resolution and only covers a portion of Wisconsin.
The NAIP imagery taken in 2006 is available for free on the NRCS geospatial gateway. So far only Brown, Kewaunee, Outagamie, Oconto, Door and Manitowoc counties have been received. The 2006 NAIP imagery is 2 meter resolution and also in MrSID format. To obtain data, you must first set up an authorized profile with the USDA. Using this profile, it possible to obtain not only NAIP imagery, but also digital topo quads, census data and other base layers.