On February 17th, 2009, every portable television will no longer be able to receive over-the-air broadcasts. If you don't know why, see www.dtv.gov

If you have one of these portable televisions, and intend for it to be an "emergency" television, you'll be out of luck on February 18th.

If you want a portable ATSC (Digital) Television, there are TWO models on the market:
7" Screen - $199

5" Screen - $149

As far as I can tell there's no ATSC tuner box that's battery-powered.

One alternative, and it's not a great one, is to get a "tuner-on-a-stick" for a laptop computer.