Examples
Intel:
Core Dual processors -- Two processors in one package sharing a common L2 Cache. 2005-2006
Intel Core 2 family dual cores, with quad core from Nov 2006 onwards
Core i7 processors replacing Core 2 family - Quad core Nov 2008
Intel Teraflops Research Chip (Polaris), a 3.16 GHz, 80-core processor prototype.
Xbox 360 game console -- triple core PowerPC microprocessor.
PlayStation 3 Cell processor -- 9 core design.
References and more information -- wikipedia