One that I need to remember to use more often is Flip Link Style. I have a habit of writing markdown links inline, but I think they look much better when they are referenced, at the bottom.
This service does as you would expect - it inverts whatever style text is currently selected.
This Service uses formd to guess what the primary format of links (inline or reference) in the document currently is and reverse it. If your document is mostly inline links, this will turn them into numbered reference links, and vice versa. It can be messy if you use footnotes.