Bukkit

Loggle Block: The combination of a Lock Block and a Toggle Block. It would behave the same way as a Lock Block, but also toggle its blocktype along with the toggle blocks it controls. Lock blocks already toggle states, so this would be pretty easy to do. The advantage is you could suspend a group of toggle blocks in the air that cannot be found with a right click and don't need to be connected to a hidden lockblock elsewhere (a line of toggle blocks that toggle from air to air are good for this).

Phoggle Block: The combination of a Phase Block and a Toggle block. State 0 is always air. State 1 is the block used as a tool to place the Phoggle Blocks (redefinable), and State 2 is definable. This would toggle between two block types and air. This would allow me to do some really really neat animations.

Sploggle Block: The combination of a Spleef Block and a Toggle block. Instead of toggling from a block to air, the Sploggle block toggles between two block types. A player can manually toggle any individual block between the two blocktypes (possibly freely and possibly only once). A lockblock toggle will force all blocks to one or the other (depending on the current state of the lock block). This would allow for some interesting player controls of machines.