You can see 9600GT SLI vs HD3870 crossfire benchmarks on this review
GeForce 9600 GT vs. Radeon HD 3870 - TechSpot
I recommend two 9600GT in SLI, and I think it is cheaper as well
EDIT
8800GT SLI > HD3870 crossfire
t-break - Crossfire vs SLI
AMD's Radeon HD 3870 X2 video card - The Tech Report - Page 7
Both reviews are more up to date than the review from expreview.com. In addition, the review from expreview is the only review I ever saw that doesn't show 8800GT SLI outperforming HD3870 crossfire
GeForce 9600 GT vs. Radeon HD 3870 - TechSpot
I recommend two 9600GT in SLI, and I think it is cheaper as well
EDIT
8800 GTS SLI > 3870 crossfire > 8800 GT SLI
but it's close between 3870's crossfired and 8800 GT's SLI'd
8800GT SLI > HD3870 crossfire
t-break - Crossfire vs SLI
AMD's Radeon HD 3870 X2 video card - The Tech Report - Page 7
Both reviews are more up to date than the review from expreview.com. In addition, the review from expreview is the only review I ever saw that doesn't show 8800GT SLI outperforming HD3870 crossfire