4. Intel 8088 (1979)
Breakthrough application: IBM PC 5150 (1981)
The 8088 began its life as a stripped-down version of the 8086 (1978) with an 8-bit bus. It functioned well with the existing array of 8-bit supporting chips required to make a working system, so IBM chose it for its new off-the shelf computer, the PC 5150.
The IBM PC is without a doubt the most influential personal computer of all time, so it only makes sense that the system's microprocessor is almost equally influential. The 8088 has been cloned more times than you can count, and its descendants, all using supersets of the 8088's x86 architecture, power every consumer PC on the market today, even Apple Macintoshes. Need I say more?
Photos: Mynikko.com, IBM