No, not another NAS, but a DAS, the N2050. This two drive box is the first eSATA DAS box that we know of.
If your machine supports S-ATA, and has an eSATA port, this should just plug in, Linux, Mac and Windows are not a problem. The two drives it can take will give you up to 1TB of storage, or more likely half that mirrored, losing a drive that big is no fun. If you want to live on the edge, you can always stripe it for speed.
The nice thing about this DAS box is that it runs at SATAII speeds, 3Gbps. If you are sick of USB2.0 or Firewire bottlenecking your transfers, the solution is finally here. This box would make a nice addition to any media center with the correct eSATA out. µ