We like cheap, well-made temperature controllers. Sure, we can make our own, but for a modest sum we can get a nice NEMA-rated package capable of reasonably complex logic with a communications interface. The Love 4C and 16C controllers can both be had for <$100 fit this description and make dependable control and higher-level monitoring possible.
The downside is that the interface is modbus over RS485, which requires a driver chip such as the Maxim RS485 which will translate to serial for control over a UART or other serial interface. This is not a killer, as you can get a nicely laid out RS485 chip from Sparkfun for $10, or make your own.
The reason for this piece is that all RS485 code I could find was designed for use with the hardware serial UART on microcontrollers such as Arduino or clones such as the Moteino. Because I typically use the UART for communication to a Pi or to a debug console, and the 328P I typically use has only one, this was not an option. To make it work over a few digital pins, it is actually quite easy to use the SoftwareSerial library to make this happen.
More details at CupidControls site.