Many of you may have this already but here it is,

Bulk Rename Utility

I see this being useful for renaming sprites and stuff. Thought there might be some of you who hadn't found it yet.

I think this kind of information should be added to the wiki or to a sticky.

For mac users, NameMangler http://www.many-tricks.com/namemangler/ does powerful bulk name editing, and you can script it and it integrates with automator.
And for the editing of text files, I use TextWrangler http://www.barebones.com/products/TextWrangler/ because it has powerful cross-document find and replace, and can check syntax in many languages.