PowerPC, short for Power Performance Computing is a RISC based archetecure created through a colaboration of IBM, Apple, and Motorolla. It was first introduced in 1992, but was a product of years of research. It is a derivitive of IBM's POWER series of microprocessors, also RISC based. PowerPC is most reknowned for its use in Apple's Macintosh family of computers, but it is also widely used by other companies in various non PC/notebook hardware.
PowerPC was derived from IBM's POWER archetecture. POWER, short for Performance Optimization With Enhanced RISC, was derived from several other projects dating as far back as 1974.
The PowerPC 601 was first used on IBM's RS/6000 workstations in 1993. Later, Apple released the PowerMac 6100, and the world was introduced to the first PowerPC processor. PowerPC was met with enthusiasm when it was first introduced to the market, but that enthusiasm faded quickly when Microsoft, and Sun customers relized that there wasn't many PPC compatable software for Windows or Solaris. Only Apple and IBM managed to profit from the PowerPC.
For a more complete list, see This list by Peter Perlso or Wikipedia's List.
POWER3 and onward follows PPC standard, all are 64-bit
mostly derived from POWER4