Just thought I'd share that Best Buy has an extended (3200 mAh + replacement door) listed for $69.99, no pictures yet and currently not in stock though. I'm having incredible battery life with my stock battery but I know others aren't so this may be a viable replacement. Although the replacement door might be a deal killer for some.
Platinum Series - Lithium-Polymer Battery for Nexus S Mobile Phones - SNB21SB
Platinum Series - Lithium-Polymer Battery for Nexus S Mobile Phones - SNB21SB