I've just released version 0.7 of AtlasMaker, a Photoshop script for generating texture atlases and tile grids. I've been using previous versions of this in my own projects for a couple of years now.

Features:

• Cross platform – tested in Photoshop CS3,CS4,CS5 on Windows and Mac OSX.
  
• Open Source
  
• Create texture atlases or tile grids for 2d games.
  
• Several image sorting algorithms. Find the most efficient one for your textures.
  
• Add a margin to each image.
  
• Custom data file export.
  
• Extendable – It’s easy to add your own rectangle packing algorithms and sorting methods.
  
  
  
  Let me know if you want any new features or find any bugs!