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While solid-state drives are great if you want performance, their capacity sucks. If you want terabytes of storage then you're either going to need to take out a hefty business loan or make use of old hard drive technology.
There are a lot of high-capacity drives out there, but currently my favorite is the 3TB Western Digital WD Green WD30EZRX. I own a number of these and find them fast and reliable. WD Green drives run cool and quiet, and help to cut your power consumption.
At $140 each, what more could you ask for?