Relay alternatives that are silent and support 500mA+
The simplest is to use a solid-state relay. You can find them from a couple of hundred mA up to 100 amps, in both DC and AC. I would look for one with a logic-level input; their input is an LED hooked to an opto-isolator, so you drive it just the way you would an LED; with a resistor hooked up to output from the microcontroller. 

They aren't cheap, however.

You can use an opto-coupler to drive a transistor to switch most DC current.