jumping spider 4-6, female -- Salticidae Dendryphantinae Metaphidippus
This is close to 100% crop. The large size will reveal some degradation in image integrity. However, considering the extreme crop, the Nikon 20mm AF-D (wonderful lens when also used in the normal manner!) delivers, and can resolve tiny details with surprising clarity even at lower magnifications.
The 20mm lens allows me to get roughly the same magnification factors (using less extension) as the 28mm. Extended to 77mm, magnification comes close to 8x if my calculations are correct. But that's a difficult setup: dark viewfinder and amplified camera shake! This deepens my admiration for those who can take tack sharp images at 10:1, handheld.
Update, 01/27/2009: ID-ed as a female Metaphidippus, possible chera sp. Thanks to Mr. Jay Barnes.
Nikon D200, 20mm reverse mounted on extension tubes (55mm total), SB800.