Pigman farming. Each portal requires 84 blocks of obsidian and the farm is going to have about a dozen portals.
Nice. I don't have that much gumption. I think the most impressive ones I have seen was the one where someone made an entire symphony orchestra from the "music" boxes or whatever you call them. I also some an awesome Rube Goldberg contraption that was like a roller coaster and its entire purpose was to create a ham.
