"Did you have a good world when you died? Enough to base a movie on?" -- Jim Morrison
Fortunately Morrison did have enough to base a movie on (the inappropriately titled The Doors), but thousands of dead celebrities and historical figures would make horrible subjects for biopics. Just because they led famous lives doesn't mean they led dramatically entertaining lives. Of course, Hollywood is good at making up or manipulating events for dramatic purpose and therefore just about any person could be given the formulaic biopic treatment.
Some people are better served with made-for-TV movie, others with big-budget studio epics. The easiest subjects to imagine are those who would provide great soundtracks; the more difficult personalities are those without current relevance or some fitting resonance today. I picked seven dead people (and a bonus: one living dog) who don't already have films in development (as far as I know) whose lives we need to see on the big screen as soon as possible.