If you've ever used NAnt, you'll love NAntPad.  From their site:

Nantpad is a powerful editor for NAnt XML build scripts. It provides an explorer-type interface saving you from having to write XML which can be tedious and sometimes difficult to maintain. User friendly icons indicate targets, tasks, parameters, comments and other NAnt entities, and attributes are modified in a property window.

I just downloaded it and loaded a few of my more complicated build scripts.  No troubles.  It helps you enforce the schemas so it's alot easier to write a script without consulting the documentation to find out the name of that one important attribute.  Me likie.