Here's the coolest gizmo to arrive so far: a Xincom DPG-402. This is a dual WAN NAT router. I already have the equivalent device from Nexland, but since they were bought by Symantec, the product seems all but dead.
This is something I am going to look into getting. Except, since I don't have a landline, I don't think I have any options for a second network provider. My one experience with Nexland is that they are terrible -- the Xincom (from checking out the website) looks like a more well-made product.