Do you miss something on BrainKing.com and would you like to see it here? Post your request into this board! If there is a more specific board for the request, (i.e. game rule changes etc) then it should be posted and discussed on that specific board.
My fellow, tenuki has just chipped in an idea: neutral discs could dissappear when they create a line of 4, making all discs above them fall down.
Another idea:
How about rhombus-shaped 10x10 board. Discs fall down diagonally (from either left or right side) and can block making part of the board unplayable and stick to other discs.