So, I finally got around to working on setting up a minecraft server, picking out mods, and getting everything working. Due to the permissions settings being mostly untested, I have yet to make it public, but so far my friends and I are building some pretty neat stuff. I'll get some pics when it goes public, but lemme give you some neat descriptions.
First thing I built was a giant windmill with blades that actually spin in a 4 frame animation. I then proceeded to build a nice park right next to it, in the area around the default spawn point that WorldGuard is protecting. My brother and I built an underwater biodome, and I gave it a fully functional vertical airlock. We then built a floating island to put his house on, where he now keeps two dogs at all times.
I am building a cemetery where all kinds of undead oddities will spawn every night (a combination of nighttime Pacific Time and nighttime in game) and that will also have a mysterious underground chamber appear underneath the chapel at the same time. The chamber is rumored to take visitors to a mysterious realm of night with scarlet stars, dead trees, and the living dead. (I'm building that deep underground, and it's going to be awesome)
Theory and I are building some other stuff. We've mostly finished a dungeon, complete with a hidden reward at the end as well as a (sorta) boss chamber. On top of that, we've built a sandstone city in the cliffs, and the closest thing I can think of to describe it is some buildings I've seen out in the Mojave Desert, specifically an architectural style based at least in part on the pueblo dwellings common in the area. Oh, and it has a giant waterfall through the middle.