Intel is currently working on the "Conroe" chip family and they have successfully put "quad-core" on the die.
There will be a desktop chip, notebook chip, and a server chip. These are due out 2nd or 3rd quarter of 2007, and all have some level of advanced power management incorporated into the chip (similar to the Pentium "M" technology).
We should see more documentation on this family (probably around Vista release, or so).
I believe AMD is working on multiple core chips, but I have only seen a passing article on the Intel "Conroe" family. Intel is hoping to prompt hardware manufacturers to build better power management capable hardware devices that can interact with the new direction for power concerns.
Not sure if this will be 64 bit, 32 bit, or both though.