It depends on how you are constructing your options for select. If you’re doing it like the code below, just pass a string into the :include blank.
select("post", "person_id", Person.all.collect {|p| [ p.name, p.id ] }, {:include_blank => 'Some text here'})
If you’re setting the options with a options_for_select(), then you can do something like the following:
options_for_select([["Dollar", "$"], ["Kroner", "DKK"]])
With the value=”” being the second value in the array and the name that shows up in the dropdown being first. So in your case, you could change the second answer to look like this:
options_for_select([["Some text here", ""], ["Dollar", "$"], ["Kroner", "DKK"]])