I tend to use notepad a lot... for me it's the digital equivalent of jotting down notes on scrap paper.  A couple things I like about it are that it has a very minimalist interface which leaves the maximum amount of space for text, and there are no worries about it being a resource hog.  However, I've been burned more than once by an untimely machine crash causing me to lose my current notes because it had been a while since I had saved.  Enter TextPad.  Like the built-in windows text editor, notepad, TextPad is a slim text editor but it adds on a few key features that come in very handy without turning into bloatware.  From the perspective of XNA game development, my favorite features are:

1) Auto-save

2) C# syntax highlighting

Below I've listed the steps I always take with a new TextPad install in order to set it up as a minimal "notepad+".  

1. Download and install Textpad: http://textpad.com/download/index.html

2. De-clutter: close the optional side/bottom panels (can always re-enable via View menu):

- Document Selector

- Clip library

- Explorer

- Search Results

- Tool Output

3. Enable auto-save

- Configure > Preferences > Backup > check 'Automatically save every N minutes' and choose how often to save

4. Enable C# syntax highlighting

A. Select Configure > New Document Class

B. Enter the Document class name, e.g. C#

C. Enter the Class members, e.g. *.cs

D. Check the box for 'Enable syntax highlighting'

E. From the dropdown menu, select the appropriate syntax highlighting template (i.e. csharp.syn, which is included with default install) 

At this point you can now open C# code in TextPad and it will be displayed with proper syntax highlighting in a barebones interface.  I find this comes in very handy, e.g. when you don't want to open another copy of Visual C#, or when you want to review some code on a machine where you don't want to install the full development environment.  If the mood strikes you, there are some things you can do to customize TextPad even further for C#:

- Under Configure > Preferences > Document Classes > C# you can set other options, such as whether to auto-indent and what colors to use

- The TextPad site has a good faq that shows how to do more advanced things like launching the C# compiler from within TextPad

Any other TextPad fans out there?