Freescale Semiconductor (formerly Motorola Semiconductor) will be introducing a dual-core PowerPC chip in October, at the In-Stat/MDR Fall Processor Forum in October. Freescale's First Dual-Core PowerPC Processor will be presented by Toby Foster, System Architect at Freescale.
No specifics are given, but such a chip might be the e600, a next generation 2+ GHz chip based off the G4 core. This chip is known to have a multicore option.
It's unlikely that such a dual-core chip would be used in Macs however. The iMac and eventually the PowerBook will be going with the G5 970FX, the former in a couple of months, and the latter in 2005. There's also the iBook and eMac, but if they don't go G5 and end up using the e600, it would likely be a single-core version.