Think of the Synology DS412+ DiskStation as a non-expandable four-bay version of the DS1512+ in a mostly plastic case.
Updated - Thecus has announced a lower power Atom-based four-bay NAS.
Synology has announced two NASes: one wireless-connected; the other aimed at professional photo storage.
The QNAP TS-569 Pro brings Intel's D2700 Atom to a five-bay platform, but little performance boost over the TS-559 Pro II.
Thecus' five-bay N5550 offers great performance at a price that won't require a second mortgage.
QNAP's TS-269 Pro can move files at near Gigabit speeds. But it could push the limit of what you're willing to spend for a two-bay NAS.
Updated - QNAP has announced a new line of Intel dual-core Atom based NASes.
Buffalo has added three biz-class Atom-based NASes to its TeraStation line.
Updated - Thecus has announced an Intel Atom-based seven-bay NAS.