First though, in order to get around the silly "rich text" default setting, when you open your HTML file, select File -> Open and be sure to select "Ignore rich text commands" as below:

You'll then see all the HTML in your file. Note: be sure to save your HTML from Safari as Format -> Page Source instead of Format -> Web Archive. Web Archive won't open properly in TextEdit.
To set this permanently in TextEdit, go to Preferences -> Open and Save -> select "Ignore rich commands in HTML files" as below:

While I'm ranting, another pet peeve of mine is Grab's inability to save to a browser-readable image format like JPEG or PNG. To capture images from a Mac for this blog, I'm forced to use Grab to save a screen capture of a window to a TIFF file and then open up Preview to convert the TIFF to PNG. This is stupid.
6/30/2007 Update: Ok. My apologies Apple Developers. I'm stupid. I did not see this feature in Preview:
/2007/06/screen-or-window-capture-in-mac-osx.html
Done ranting.