There seems to be very little covering Fireworks anymore! Those few I have seen in Amazon don't get exactly stellar reviews (although with so few reviews that is easily skewed!)
I see:
Marcromedia Fireworks 8: Training from the Source through Adobe/Macromedia
Marcromedia Fireworks 8 Revealed
Learning Marcromedia Fireworks 8 (Pricey)
The rest are Macromedia Studio and Dreamweaver/Fireworks books.