I've always been a fan of Notepad2 as a replacement for Notepad. I spend a fair bit of time editing Inmagic Genie XML config files and the features like line numbers and XML syntax highlighting make this so much easier. However I've just switched to Notepad++ which allows multiple documents to be open in tabs. As I usually have at least 3 or 4 config files open at once, this in itself is a great time saver.
Notepad++ also includes plug-ins for tools like HTML Tidy with an option to clean up the junk that Microsoft embeds when saving a Word doc to HTML. There is a file compare option - useful when reviewing Genie config files from a client to see what they have changed, plus there are a stack of other options that I haven't even looked at yet!
Notepad++ is open source software and is available for download from
Sourceforge.net. There is also a version available that runs from a USB stick at
PortableApps.com.