Pau ferro, Macherium villosum, also commonly known as Morado or Bolivian rosewood makes a very nice bass fingerboard, as well as a pretty nice sounding dreadnought guitar back and sides. Sometimes you may aso find Caesalpina ferra marketed under the same name. Keep in mind that it does cause allergic reactions in some poeple.
There is a two part article series in American Lutherie magazine last year from my plywood bass restoration workshop at the last Guild of American Luthier's convention that discusses and shows a photo sequence of me building a Pau Ferro double bass fingerboard. I often use it as a substitute for Brazilian rosewood, d. nigra. It looks very similar, handles very well, and is a pretty dry wood in that it does not have nearly the oils that some of the other rosewoods have. Hence, your sander and such will not load up withoils and resins when you use it. It works very well, is in easy supply, and you can find it with very nice quarter and grain.
Like d.nigra, it is also much softer that ebony, so expect it to wear a little faster if you are an aggressive player and slap a lot (like me!!!!).
I can also get it somewhere in the neighborhood of $8 per board foot locally! Most of what I have seen commercially available has had some form of kiln drying, so look out for irregular stress checking. The longer you can air dry it, the better. I've got some wood in my shop that is over 100 years old and you can definitely tell a difference between that and the recenty cut wood.
If you already have the wood in hand, use what you have. Whenever I buy wood in the rough form to make new fingerboards, I usually prefer at least 6/4 or 1 1/2" thick minimum. Better to have a bit extra than to be a little thin.
j. www.condino.com www.kaybassrepair.com