A complex consisting of domes and spheres created in the Structure Planner. Built entirely by hand within Minecraft.
A 120m wide suspension bridge designed in the Structure Planner, exported as a .schematic file, then imported to the world through MCEdit. If you've not tried the world editor MCEdit before, go download it and give it a go. It's an excellent piece of software!
An underwater rectangular dome designed in the Structure Planner and built very slowly and with much drowning, by hand.
This 50m x 50m castle is actually a spawn-trap. The Structure Planner was used to map out how the water channels inside the trap channel mobs to the drowning chamber, and also provided construction plans for the arched supports underneath the main walls.
This ridiculously simple ranch house holds sentimental value for me as it was the first structure fully designed in the Structure Planner Freeform tool, and then exported/imported directly to my game world.
A 61m x 61m 'Recursive Backtracker' maze with internal walls of 2m high cobblestone and external walls of 3m high stone. Construction of this monster would have taken 3,364 cobble and 720 stone. Luckily this one was imported directly into the game world!
The 'Trinitis Cube', named in honour of the Redditor who found the Obsidian export bug, is a Level 3 Menger Sponge generated entirely using the Structure Planner and MCEdit. The cube consists of 8,000 blocks of Obsidian, which interestingly enough would take almost exactly 42 hours to mine manually according to a statistic that I just made up.
This 'Superman' logo was created with the new 'Pixel Art' tab. It was about ten minutes work to design, and another couple of minutes to export and import into my test game world.
Created on the Gargemel seed world, the Budd'oh was designed in the Pixel Art tab, then carved into the cliff and built by hand.