Samsung HD103SJ SpinPoint F3 1TB SATA-II

I've owned about 6 of these drives over the last two or three years and they've all been excellent. No failures, despite heavy usage, fast, and excellent value for money. Just purchased another four from Aria.co.uk, and they were delivered less than 24 hours after ordering.

Just make sure you order some SATA cables at the same time, because most places don't include them.