Andrews, B. “What Are Galaxies Trying to Tell Us?” Astronomy (February 2011): 24. Introduction to our understanding of the shapes and evolution of different types of galaxies.
Bothun, G. “Beyond the Hubble Sequence.” Sky & Telescope (May 2000): 36. History and updating of Hubble’s classification scheme.
Christianson, G. “Mastering the Universe.” Astronomy (February 1999): 60. Brief introduction to Hubble’s life and work.
Dalcanton, J. “The Overlooked Galaxies.” Sky & Telescope (April 1998): 28. On low-brightness galaxies, which have been easy to miss.
Freedman, W. “The Expansion Rate and Size of the Universe.” Scientific American (November 1992): 76.
Hodge, P. “The Extragalactic Distance Scale: Agreement at Last?” Sky & Telescope (October 1993): 16.
Jones, B. “The Legacy of Edwin Hubble.” Astronomy (December 1989): 38.
Kaufmann, G. and van den Bosch, F. “The Life Cycle of Galaxies.” Scientific American (June 2002): 46. On galaxy evolution and how it leads to the different types of galaxies.
Martin, P. and Friedli, D. “At the Hearts of Barred Galaxies.” Sky & Telescope (March 1999): 32. On barred spirals.
Osterbrock, D. “Edwin Hubble and the Expanding Universe.” Scientific American (July 1993): 84.
Russell, D. “Island Universes from Wright to Hubble.” Sky & Telescope (January 1999) 56. A history of our discovery of galaxies.
Smith, R. “The Great Debate Revisited.” Sky & Telescope (January 1983): 28. On the Shapley-Curtis debate concerning the extent of the Milky Way and the existence of other galaxies.
ABC’s of Distance: http://www.astro.ucla.edu/~wright/distance.htm. A concise summary by astronomer Ned Wright of all the different methods we use to get distances in astronomy.
Cosmic Times 1929: http://cosmictimes.gsfc.nasa.gov/online_edition/1929Cosmic/index.html. NASA project explaining Hubble’s work and surrounding discoveries as if you were reading newspaper articles.
Edwin Hubble: The Man Behind the Name: https://www.spacetelescope.org/about/history/the_man_behind_the_name/. Concise biography from the people at the Hubble Space Telescope.
Edwin Hubble: http://apod.nasa.gov/diamond_jubilee/d_1996/sandage_hubble.html. An article on the life and work of Hubble by his student and successor, Allan Sandage. A bit technical in places, but giving a real picture of the man and the science.
NASA Science: Introduction to Galaxies: http://science.nasa.gov/astrophysics/focus-areas/what-are-galaxies/. A brief overview with links to other pages, and recent Hubble Space Telescope discoveries.
National Optical Astronomy Observatories Gallery of Galaxies: https://www.noao.edu/image_gallery/galaxies.html. A collection of images and information about galaxies and galaxy groups of different types. Another impressive archive can be found at the European Southern Observatory site: https://www.eso.org/public/images/archive/category/galaxies/.
Sloan Digital Sky Survey: Introduction to Galaxies: http://skyserver.sdss.org/dr1/en/astro/galaxies/galaxies.asp. Another brief overview.
Universe Expansion: http://hubblesite.org/newscenter/archive/releases/1999/19. The background material here provides a nice chronology of how we discovered and measured the expansion of the universe.
Edwin Hubble (Hubblecast Episode 89): http://www.spacetelescope.org/videos/hubblecast89a/. (5:59).
Galaxies: https://www.youtube.com/watch?v=I82ADyJC7wE. An introduction.
Hubble’s Views of the Deep Universe: https://www.youtube.com/watch?v=argR2U15w-M. A 2015 public talk by Brandon Lawton of the Space Telescope Science Institute about galaxies and beyond (1:26:20).