Who knew?! Thanks to this macosxhints.com article for pointing out a cool feature in the 10.4/Tiger version of TextEdit: a built-in outliner.
While in RTF mode, on any blank line, hit Option-Tab to create a list item. Hit Return for the next item and so on. Additional Option-Tabs will increase the indentation; a Return on a blank list line will decrease it.
It uses hyphens to indicate list items by default. Right-Click (or control-click) to choose all kinds of “List…” styles.