I have a project called iSprite at http://iSprite.codeplex.com
In a jist it allows you to create a grid and place images in that grid through drag&drop, or inserting multiple files. When you click save it produces a sheet with all drawings centered exactly based on the original size image. Each square has attributes that can be modified
I'm working on adding save folders, so multiple sheets can be stored with an xml definition file.
If anyone wants to use it, help code it, etc..., I would greatly appreciate it. Currently I make improvements as I need them. After all the features are flashed out I plan on adding a multi layer level editor.
The app is developed in .net (PC).