I have made a return to Minecraft, and have decided to restart with a big map. This is an 800x600 block wide map, and took about three months to complete by myself. All of the terrain was created with a combination of WorldEdit and Voxel Sniper. I didn't build the trees, but these wonderful people have made their trees up for public use.
Custom tree pack Vol. 1 By Murokmato
Keno's Tree Repository By kenofox
Tree Bundle [Medium] + Download By Team Surface