Might as well add my map to the ever-growing pile...
Agartha: Symmetrical team game map, with a 4-level base structure, ideally meant for CTF and Assault.
Diagonal view of the map, you can see all 4 levels from this point. There are two side doors on each base leading to the basement, where there's a shotgun and a Brute shot.
Above the basement is the main level, where a Regenerator, a couple plasma grenades, and a bunch of rifles spawn. There are two ramps leading up to the level above it, where a needler, a Power Drain, and a few more rifles spawn. There are two more ramps on either side leading up to the top level, where a sniper rifle and the flag spawn.
In the center of the map, at the bottom of the main ramps, is a block with rockets on it. On either side of the center section is plenty of cover, including two of the bunkers that hold a bubble shield each, and a bunch of weapons strewn about. On the two pillars (below), an Active Camo spawns. The bunkers are slightly offset from being perfectly centered, so one is slightly closer to a given base than the other, to encourage a circular flow around the map.
Lastly, here's a basic overhead view that sort of gives a good impression of the map's scale. I wouldn't figure that more than 5 or 6 per team would work well on it, but I haven't had a chance to get any games going on it.
Here's a link to my fileshare:
http://www.bungie.net/Stats/Halo3/FileShare.aspx?gamertag=Havok CXVII where I have it and two of my other (Foundry) maps, which I am fairly proud of, so if you like this one you might want to give them a shot.
My gamertag is Havok CXVII, if you guys want to play a few games give me a shout, its been great getting matched up with HaloGAFfer's in the Mythic playlist over the last few days.
A few thoughts on the Sandbox Forge experience: The budget is a lot lower than I had initially thought, and I ended up depleting the object count even after using all of the default objects. I'm not sure how large maps are going to work in the sky bubble if there aren't enough objects to make big bases, especially since the spawn points count as objects (which I really dislike, I ran out of objects right in the middle of placing spawns). Also: The walls of the crypt are not perfectly straight, there are large horizontal mounds on them, which creates almost as many problems as the uneven walls on Foundry did...I don't know, it just seems kind of silly that the walls aren't 90 degrees all the way down when it would help out so much.
Edit: Ghaleon, if you want some folks to run around your map and try it out, I'll probably be on for the next few hours.