Celestial Navigation website: http://www.celestialnavigation.net/. Has history information and other links.
Celestial Navigation website: http://www.math.nus.edu.sg/aslaksen/gem-projects/hm/0203-1-10-instruments/home.htm. Originates from math department of the National University of Singapore. Includes information on instruments, with links to other sites.
Nautical Almanac On-Line: http://www.tecepe.com.br/scripts/AlmanacPagesISAPI.isa. Includes many years of nautical almanacs and provides a star finder.
Navigation in the days of John Cabot: http://www.heritage.nf.ca/exploration/navigate.html. Shows navigational instruments of the 16th century, as used in voyages to Newfoundland by John Cabot.