I started out making this by making a massive underground room 50 by 50 by 2 blocks.
Next I began digging trenches around the edges of this massive room that were to be filled with water. For those unfamiliar with mob traps, the mobs spawn in the big room and then fall off the edges and are swept away by water currents.
This is the room with the completed trenches and the the water flowing.
Next I added some more trenches that are kinda elaborate and I couldn't get great screen shots of them so I decided not to include them. However these trenches all lead to a funnel type thing that I do have included.
Again if you are unfamiliar the funnel is made of glass because for some reason Notch decided that if mobs are swimming next to glass they will sink instead of float. So when the mobs come into the funnel they sink, drown and whatever items they drop are swept away to the collection area shown below.
Bonus pic! As I was building this structure I discovered a massive cave system that I got five diamonds from so far.
So that's pretty much it. A chronicle of my Oxycontin fueled Minecraft endeavor. I collected a lot of materials from this build so if anyone has some suggestions for something I should build feel free to let me know.