There is also the Arduino Mega, has 50+ i/o, Several Analog channels, PWM, multiple communication interfaces, you can drive all kinds of electronic devices: LCDs, Graphic touch screens, steppers, MPG's (encoders) motors, etc. Basically everything the PK can do plus more, and you have control over the code, and the hardware, and it is MUCH cheaper you can get them at the local radio shack.
I have one here that I use to run 5 steppers, Spindle (pwm with analog feedback), with a LCD/Graphics touch screen, matrix keys, some spi driven devices and you can chain them with the multiple serial I/O channels.
I set up serial coms with it by using the source code that Brian released to do a Serial plugin, just added in my I/O commands to/from it.
Like any thing, what you choose to use will depend on how much you want to have control over, verses having someone else do the work for their product for you.
Scott