Inspired by a design by APTD in his video here: http://youtu.be/J8PwKDISKYU
Also using a glass drowner designed by Brewtalizer which exploits the way water flows across glass to force the mobs to float in an air-pocket where their heads are stuck in water and they drown (even spiders). This is the same drowner I used in my huge drowner trap here: http://www.planetminecraft.com/project/flyingpenguin33s-trap-using-a-drowner-by-brewtalizer/

(Note: 1.7.2 update slightly altered the way the glass drowner works. The first spider always ends up on the bottom of the trap and doesn't drown, but all subsequent spiders land on top of him and eventually drown).

This trap was built on Poopiepant's Build Server Aug 2011 using WorldEdit.

I've made a WorldEdit/MCEdit schematic available. The schematic was saved at the bottom west side of the pit, facing east. The whole structure is about 80 blocks tall.

The texture pack was designed by one of our members, Drexul, and we call it the DREXULPACK. It requires MCPatcher to enable Minecraft to work with 128bit & 256bit textures. Get MCPatcher here: http://www.minecraftforum.net/topic/232701-611-update173-compatible-mcpatcher-hd-fix-210-02/

The DREXULPACK texture pack is available here: https://skydrive.live.com/?cid=8BF91F07C51D2E6D&id=8BF91F07C51D2E6D%21107#cid=8BF91F07C51D2E6D&id=8BF91F07C51D2E6D%21114