Bringing order to the zoo of galaxies

Before we start doing any calculations, it might be a good idea to look around us and make an inventory of what types of galaxies are out there. There are many good web pages to start, for example I like http://www.taas.org/gnto/astropic.html, because it shows pictures made with a small telescope - so those are galaxies as you might have seen them yourself, if your an amateur astronomer. http://www.aao.gov.au/images.html/ is very nice as well, it shows professional images. If you look at the more professional pages (such as the HST archive for example), beware of an amusing bias: professional astronomers tend to observe (and make picture of) unusual galaxies.