You could also get an APC PDU 7900 or 7901 from ebay, they're really expensive new but I've gotten used ones as low as $50-$60 shipped. Sometimes the 7901's are cheaper because they have the 20 amp plugs which most people can't use at home, but you can always replace the plug for $10 (and refrain from plugging over 12 amps into them if on a 15 amp circuit
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Then, you can remotely switch any of the outlets on and off, you also get nice monitoring of your total amp load so you can calculate wattage at any time, and you'll be able to control any additional accessories as well (say you have an auxiliary fan plugged in but it isn't always needed, you'd be able to switch it on and off remotely). Another nice bonus is that you can set email alerts for when the amperage goes above or below a certain level. So if something happens, say your mining pool is down or your miner crashes for whatever reason, your GPUs would stop mining and the amps would drop way down, the PDU could let you know there's an issue...