A list of significant length is often best served by search.

Only if you know the options in advance as the sibling comment says.

And mostly for very significant length (e.g. "all my songs") E.g. for up to 20-30 items dropdown is still better, and you can select with one finger without much concetration.

Of course there's also the "searchable dropdown", or a dropdown where you can type the first letter(s) of an options to jump there.

Unless -of course- you don't have a good idea of what it is that you want to search for!

This happens to me far more frequently than I would like. :)

At which point a search with instant feedback is still often far better than trying to scan a huge list.

Not really. If you don't know what you're looking for, search with instant feedback wont work, because while you might find something, you don't know if you missed a better option (under another starting letter or substring).