Cradle:
Mobi Products Cradle w/ Spare Battery Slot for HTC Google Nexus One - HTC Google Nexus One Charging Docks - Nexus One Forum Store

Battery:
Seidio Innocell 3200mAh Extended Battery for HTC Google Nexus One - HTC Google Nexus One Batteries - Nexus One Forum Store

Will the battery fit in the dock while inside the phone and the battery slot?

Also, while I'm here, what's a good screen protector for the phone?

Thanks!