It looks like the other "name brand" NAS folks are content to see how Buffalo does with the TeraStation, since they're generally sticking with single-drive products. The exception is NETGEAR's soon-to-be-released SC101, which will be a BYOD product supporting two drives. But it's not a true NAS, since it will require a client app that runs on WinXP or 2000 only.
The only direct competition I see right now is the ReadyNAS 600 from Infrant Technologies. Although it's pricier at $1,395 for a four-drive 1T configuration, it uses SATA instead of IDE drives and other hardware features that could give it a performance edge over the TeraStation. But while it has two USB 2.0 ports, they support only USB printers for the built-in print server and can't support USB drives for storage expansion or backup.
So if your appetite for storage is big or if you're looking for the added data security that RAID 1 or 5 can provide, the TeraStation could be just what you need. You'll need a fat wallet to get into the TeraStation club, however, even at the bargain price of $1/Gigabyte.