PIC

The PIC microcontrollers are one of the most popular 8-bit microcontrollers.
Microchip have hundreds of different microcontrollers from the tiny SOT23 package to 84-lead PLCC.
They can run up to 40 Mhz and execute instructions at four clock cycle.

PLUS:
They are cheap! The low end devices (PIC10Fxx) cost $0.40/ea in volume.
Free MPLAB development tool is available for programming in assembler. There are plenty of low cost development programmers etc.
Great chioce from many devices available with difference memory size and peripherials.
GPIO ports source 20mA and can drive direct LEDs etc.
The old OTP 'C' parts are one of most reliable controlers available on the market.
PICs are available in automotive temperature range -40+125C

MINUS:
Writing in Assembler is art of programming as there is no software stack, paging, GPIO read modify doesn't work on the early PIC16Fxxx series.
Some new flash devices have hardware bugs (which urfontunately apply to all other vendors as well) and are not so reliable as old OTP devices.
No compatibility between different PICs and you have to re-write your code every time you move from one PIC to other.