From the "what if?" department....
At least one report claims that we'll see a 20" iMac as early as tomorrow (Nov 18th). Whether this design would incorporate the rumored case redesign or simply a top-heavy version of the current iMacs is not clear.
Previous rumors have pointed towards 19" iMacs... but have not yet materialized.
Last week, there were rumors that significant announcements would be made this week.