OK, so we know Olivia Colman will be the Queen and Helena Bonham Carter is probably going to be Princess Margaret. I think they're both great choices and look forward to seeing them.
Who can we cast in the other roles?
I understand the series is meant to cover the 70s, and it's been suggested that the natural "end" to the series is Thatcher's election. So we probably won't see Diana or Fergie yet, but could see Camilla.
Here is where I'm at in my head right now:
Prince Philip (fair-haired male, mid-40s/mid 50s in age): not my idea but I think Iain Glen is absolutely inspired
Queen Mother (short, dark-haired female, 60s-70s in age): Imelda Staunton, Celia Imrie
Prince Charles (dark-haired male, mid 20s/mid 30s in age): Jonah Hauer-King (he played Laurie in Little Women)
Princess Anne (fair-haired female, mid 20s/mid 30s in age): Emilia Clarke (she'd kick some ass!)
Ted Heath (grey-haired male, mid 50s in age): possibly Samuel West (who, it must be noted, has already played Ted Heath, in a drama about the young Thatcher)
Harold Wilson (grey-haired male, mid 50s in age): for some reason I'm thinking Matthew MacFadyen could be good, though he may be too young
James Callaghan (grey-haired male, late 50s in age): Timothy Spall maybe?
Margaret Thatcher (fair-haired female, 50s in age): Jemma Redgrave, Emily Watson, Samantha Bond (who would be my first choice)
That's all I've got for now, though there must be a way to fit Peter Capaldi in as someone's private secretary. Give me your ideas!