If you want easy with absolutely no setup time then I guess you can't really beat the mbed module.

It has loads of interfaces like multiple serial ports, I2C, CAN, multiple SPI, ethernet and the regular analog/digital GPIOs. You "program" it by plugging it into a computer and it appears as a drive. You just copy your compiled code over as a regular file and thats it.

The odd part is that the compiler, IDE and even your source are actually hosted by the mbed website. From what I can tell, it just uses GCC anyway and people have managed to get their own compiler running locally but I'm unsure what they do about the libraries.

The other downside is that the module is fairly expensive and its not very easy to transfer your project into something smaller or less expensive.

mbed was started by two ARM employees and is now actually run by ARM according to their about page.