The CEPII has a new database on equilibrium exchange rates for 180 countries since 1973. You can read more about their methods here. Such data is useful for examining currency misalignments, especially comparing it across countries.
I poked around it a bit to see what the Nigerian story is.
The interesting thing is the volatility, at least compared to Malaysia and China. We seem to have wild swings from a really over-valued naira to an undervalued naira and back again. Tells the story of our currency problems eh?