Bukkit

Overview:
"Falling Blocks" are just sand blocks, retextured to look like other blocks, (Similar to how blocks' textures can be changed in a Resource Pack) such as bricks in the examples below. This plugin allows you to place them in a certain spot, and keep them from being affected by gravity, TNT explosions, or whatnot.
This plugin allows you to have:
- Non-solid blocks (able to be walked through)
Can be used to create secret entrances, or things of the sort.
Example: http://youtu.be/EQLRW4iuJu4
- Any block able to glow (place a torch and create a FallingBlock in its location)
Can be used to light places where torches and other lighting sources would look awkward.
Example: http://i.imgur.com/jqFWPBB.png
- "new" blocks due to differences in rendering when creating FallingBlocks.
Example: http://i.imgur.com/A5DKvSg.png

Instructions:
Left click with wooden shovel - Turn block into FallingBlock.
Right click with wooden shovel - Turn FallingBlock into normal block.

Commands:
/toggleEnabled or /te:
Toggles if falling blocks are shown. Disabling this allows you to place a block inside a normal falling block, and then toggle it back to enabled.
/spawnFallingBlock or /sfb:
Basically the same as left clicking with a shovel, except it spawns the block you're looking at at your location, instead of the block's location. Useful if you want to spawn a block you can't break, such as water.

Permissions:
PlaceFallingBlock.toggle_state - /toggleenabled
PlaceFallingBlock.create_with_command - /spawnfallingblock
PlaceFallingBlock.create - Left click with wooden shovel
PlaceFallingBlock.remove - Right click with wooden shovel
[Operators have all permissions]

Config:
SendMessageOnCreateOrRemoveFallingBlock - True to send messages, false to not.

TODO:
- Moving blocks
- FallingBlocks on non-integer coordinates
- Reduce ram usage

(Based off of SpaceYavin's request - http://forums.bukkit.org/threads/placefallingblock.166432)