Do you really need font support for that, though? I've found editor support for it much cleaner -- it knows when it's best to expand then and when they should be ligatured.
They're usually grouped into features: standard ligatures (liga), discretionary ligatures (dlig), historical ligatures (hlig), contextual ligatures (clig), and so on. OpenType fonts can also provide stylistic sets, which might swap out some glyphs with alternatives.
I’m far from an expert, though; I’ve just gotten so used to having ligatures over the past few years that I now find it uncomfortable not to have them.