That depends on where you sell it. Ebay might bring you more money then selling it locally on Craigslist. Have you looked at auctions on eBay? That could give you an idea of the high end value. You need to look at Apples refurb prices and adjust accordingly. After all a refurb has a one year warranty.
I'd say the old macbooks are worth around 600-700 dollars. IF you upgraded it a little, like ram, bigger HDD. If not, 500 is ur best bet.
really depends on specs and condition but yea macs hold the value decently so you should be in that pricerange easily
ref26 - if you are wanting to sell your BlackBook, then you need to base your price by comparing to the $1099 Apple refurb price. Put yourself in the position of a potential buyer. With the Apple store you get a one year warranty and BlackBook in the box with all accessories. Now look at your used laptop and what does it include? You need to adjust your price down to compete. Having said that I still see people on Craigslist listing old white MacBooks for $1000 and old G4 PowerBooks for $600-700. So you can always list it and see what happens.