The Canon EOS 1-Ds has been the only full-frame 35mm digital camera since the failed Contax N Digital introduction and the resignation of Kodak. While Nikon is still struggling to develop a full-frame camera, Canon has already released a mid-level full-frame camera, priced at $3,300, below the cropped Nikon D2X.
With the EF-S line-up and the excellent 10-22mm EF-S lens, the need for full-frame solely for wide-angled shots is not as important as it was before the EOS 20D. The EOS 5D, with its full-framed sensor, does provide greater depth of field. Analysis in the Web reviews indicate that there's no improvement in dynamic range or noise over the cheaper APS-C EOS 20D, but it does provide better resolution with its 13MP sensor.