The 16F84 family
PICs (Peripheral Interface Controller) from Microchip are, perhaps, the most popular microcontrollers. The most useful feature of this microcontrollers is that they are flash based (so they can be re-programmed many times), cheap, robust .....
16F84 is a minimalist uC which is ideal to start learning microcontrollers. There are tons of ressources for this uC (tutos, simulators, circuits .....) on the web. Pinguino is an Arduino-like electronics prototyping platform. It supports different PIC icrocontrollers, all with built-in USB module (no FTDI chip !). Pinguino comes with a USB Bootloader. This small program running inside the microcontroller is responsible for transferring your application from your PC to the microcontroller memory and handing over the control to this program afterwards. No programmer is needed(*), the microcontroller can be reprogrammed over USB with a PC. Just like Arduino , there are many versions of Pinguino using different Microcontrollers from Microchip.
18f family has a built in hardware USB module very useful if you intend to interface your project with a PC.
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Ressources:
pigonof: Excellent place for french readers.