HD Radio continues to gain momentum as more automakers announce availability on more new cars. Most recently, Mercedes-Benz and Hyundai announced HD Radio options. For Mercedes, it's available on the M-, R-, GL-, G-Class SUVs and E-Class sedan. On Hyundai, it's on the flagship Genesis sedan. HD Radio allows a broadcaster to have up to three digital broadcasts while continue to broadcast in analog FM or AM as well. Once you buy the radio (or adapter), it's free, unlike satellite radio, but it's also not free of commercials.

With the recent announcement by Mercedes-Benz of factory installs of HD Radio receivers on select 2009 model-year vehicles, the list of automakers offering factory install grows to nearly a dozen. Those who announced offerings of HD Radio receivers as factory-installed equipment are
BMW Group -- entire BMW line, Mini
Ford - all Ford, Lincoln, Mercury
Hyundai - Genesis
Toyota - Scion
Volvo - C30, C70, S40 T5, S80, V50 T5, V70, XC70 and XC90
Jaguar - XJ

Replacement car radios with an HD tuner include models from Alpine, Boss, Dice, Dual, Insignia, Jensen, JVC, Kenwood, Pioneer, Sony and Visteon.

Cheap in the aftermarket (less so on new cars)
Many replacement radios offer a CD player and the HD Radio tuner (plus AM/FM) for less than $200 and now with royalty-holder iBquity reducing the rights fees, replacement radios (some of them) may approach $100. Unfortunately, on new cars HD Radio is often a pricy option, costing $350-plus for the radio upgrade, or as much as 10 times as much when it's part of a package. For Mercedes, HD radio is part of a P1 premium package that costs $3,000-plus. On BMW, HD Radio is available separately, but it's $350 and must be installed at the factory. Ford offers a reasonably priced dealer-install HD Radio if the car doesn't come equipped.

If you're looking at add-on tuners, be sure to check whether the tuner can be controlled by your existing radio and if the station information shows up on the dashboard radio.