There's always HPNA and MoAC. Coaxial lines are robust stuff. These devices work like tiny cable modems, which mean you can't use a real cable modem on lines also used for an HPNA network. It can share TV signal though as these are different frequencies. Beyond that though, you can get upwards of 300Mbps on the quality stuff. The really good ones come with a coax pass through, two ethernet ports, and a WiFi AP to extend your wireless network.
Then there's doing the same thing over phone lines. Cat3 or voice grade 4 conductor can handle this stuff too, but don't expect much out of that. It can work reliably, but it will be slow. My father has a decent one of these running, and I think he said upwards of 30Mbps between the nodes.
