Logos can be found on the Debian logo guidelines page at: http://www.debian.org/logos/
The official logos have been selected by vote of the Debian developers in Mid 1999.
They have been created by Raul M. Silva (http://www.silva.com)
Get banners to show your Debian pride at:
Read the Debian Graphics blog here:
http://www.linuks.mine.nu/volkany/
BTW, the font used to write "Debian" in the logo is a payware font called Poppl Laudatio Condensed. The i-Dot has been manually replaced by a red diamond. Julien Blache annotated that the text has been condensed horizontally and stretched vertically. The text can be found in vector format at http://www.debianart.org/cchost/?ccm=/media/files/si0ux/59.
There was also a resemmbled free font at http://www.flyerstarter.com/Free-Fonts/L/Laudatio-C.html - a page that still hosts it is http://www.abstractfonts.com/fonts/search/full_listing.htm?kw=LaudatioC
Unofficial/Alternative Logos
Some unofficial, alternative Debian logo art is available at http://alphapapa.net/debian/logos/, with some previews viewable at http://alphapapa.net/debian/logos/gallery.html