The Cell microprocessor is frequently credited to IBM, although Sony and Toshiba are also significantly involved in the chip's development. The project (and the company alliance) was announced in 2000, and the project lasted four years. Currently the architecture is "finished" if not highly in-use.
The Cell architecture is intended to be highly scalable, usable for the simplest and the most complex of computing devices. Conceptually, it consists of an array of processing units around a central processing core - a 64-bit PowerPC core. The satellite units are what makes the architecture scalable, and chip design has taken heavy considerations toward things like power consumption and ease of programming.
Although the Cell is touted to be an end-all-be-all microchip for even the most powerful applications, e.g. weather and disaster prediction, the PlayStation 3 is currently the most exciting thing anyone plans to use it in.