Gridder is a tool definitely missing in After Effects, it allows you to arrange layers into the customizable grid in many ways.

Copy the file "Gridder.jsx" into the following folders:

Windows: C:\Program Files\Adobe\Adobe After Effects CS[x]\Support Files\Scripts\ScriptUI Panels

Mac: /Applications/After Effects CS[x]/Scripts/ScriptUI Panels

You should allow scripts to write files Edit->Preferences->General->Allow Scripts to Write Files and Access Network