Great idea!
There's
in_variance, a RP comm
formerly on LJ. It has yet to start, but might become active after they have finished RP-ing the second day.
PS. Are you listing only the comms moved here from LJ, or all comms (including the ones which began here on insanejournal)? If so, there's a comm knowns as
dear_you for writing annoymous letters to vent, and
journalwhore, a comm dedicated to sharing codes from other LJ clones. There's also
ijdesigners (which hasn't been updated since 2004), but
stylemonkeys seem to be its successor (no posts yet, to date). There's also
howto, which is supposed to provide styling tutorials, but it's also not been active since 2005.