Many MCU applications use electro-mechanical relays to control AC loads. While this is an excellent solution for occasionally turning on/off a load, it is not suited for frequent switching or PWM applications. SSR1/A is an opto-coupled solid state relay that can control two AC loads in a arduino shield form factor.
Despite the significant advantages in size, weight and efficiency, switching AC-DC supplies are not very common with hobbyist due to their complexity and scarcity of ready to build kits.
PWR01 is a low power (~6W) universal voltage (100-240V) isolated AC-DC flyback converter based on the ST Microelectronics VIPer17. Either 5V or 12V output can be obtained using an off the shelf transformer.