In BBEdit on the Macintosh:

  • Hit Command+F for Find...
  • Tick the box beside "Use Grep"
  • Enter "$" in the "Search for..." box
  • Enter "<br>" in the "Replace With..." box
  • Hit the "Replace All" button

Et voila! I count eight keystrokes/mouse clicks in total, making this easily as efficient as vi/command line jiggery pokery, if not quite as satisfying.

Addendum: to replace tabs with <dd>s, simply repeat the steps above, substituting "\t" for "$" and <dd> for <br>.