As far as I know, the 640GB WD drives are still dual-platter. Also, the "Black" version of the drives should be geared toward slightly faster performance than the normal "Blue" version, but at the expense of slightly more noise and heat, in addition to a typically higher price. They also come with a 5 year warranty instead of 3, though I doubt their reliability is much different, and you should make sure you back up important data either way. I've been using a 640GB Blue drive (though it wasn't called "Blue" at the time) for a few years, and it's performed rather well. I can't really provide any personal suggestion on which among the current 7200 RPM single platter drives is quietest though, aside from what could already be found in reviews.
Another option, if you don't need much space and are willing to pay more, would be to look into an SSD, which should be completely silent, and if it's a decent one, much faster than any hard drive.