Shields are good for major building blocks like Ethernet and CELL Modem. But maybe for relays and the other things you may connect in the home for Automation, like temperature sensors, lighting and heating controls etc etc., it may be better to leave that more open-ended.
My favorite "top" shield is the "Sensor Shield" , AKA the "EZ-Connect Shield". See: http://arduino-info.wikispaces.com/SensorShield
DISCLAIMER: Warning, mentioning stuff from my own shop... but that's what I know best.
You can connect many different relay boards and DC power control boards with simple cables: http://arduino-info.wikispaces.com/ArduinoPower
And various sensors like: http://arduino-info.wikispaces.com/Brick-Temperature-DS18B20
This way most connections are made with good cables that are more secure than breadboards and wire jumpers.
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