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.
(gem) Træt af at skulle klikke dig igennem 2-3 side for at komme til den samme side. Betalende medlemmer kan tilføje det til deres kontekst menu. (pauloaguia) (vis alle tips)