The current
Astronomy has a brief article about what makes a comet "great". David Eicher gives a list from the mid-1960s on...Ikeya-Seki, West, Hale-Bopp and Hyakutake.
Donald Yeomans has an interesting article at the JPL website. He agrees with Eicher's enumeration of recent great comets, although he adds McNaught (2006 P1). Interestingly, Yeoman's historical list of great comets accompanying the article shows a glaring gap from 1927 to 1965, reminding us that Mother Nature has no requirement to satisfy our craving for bright comets. That gap is basically half a human lifetime, so if ISON (or any other comet) puts on a good show while you are still around, by all means see it while you can!
More information:
Astronomy, August 2013, p. 9
http://ssd.jpl.nasa.gov/?great_comets