I bought one of the underground sprinkler controllers and the controller power supply in an above ground solution. I connected a short piece of water hose from the spigot to the controller and then from the controller to the sprinkler head. I control the sprinkler controller using an X10 appliance module.
I've been looking for somehting similar as I live in a cold climate and have ledges around me - kinda hard to bury sprinkler systems deep enough to prevent freezing in solid rock!
I found the light-duty Orbit valves and timers work fairly well ($15 for the valve at Home Depot), and though I've been using them with a timer and manifold ($45 for a kit at Home Depot), they certainly look hackable (they plug into the timer unit with a stereo 1/8" plug and use a pulse of power to flip the valve open or closed). The timer works from 3 AAA batteries and has decent features, so one of these days I'm going to hack these for use with an HA system. Right now I have two of them and they are working perfectly.
I took the extreme low-buck route: I used the hot/cold water valves from an old washing machine and ran the wire to a couple of X10 appliance modules. We're getting a new lawn and an underground sprinkler system this fall so I'll be retiring it to some other purpose, but it has worked well for almost three years now.
CAUTION: If you do this take extra care to isolate the wires from the water as you're dealing with 120V!!