The Very High Frequency (VHF) band is the segment of the television broadcast band covering channels 2 through 13. The Ultra High Frequency (UHF) band is the segment of the television broadcast band covering channels 14 through 83. Currently, the vast majority of TV stations broadcasting in digital are using UHF (14 and up) channels to do so. This is not due to any technical requirement of digital broadcasting, however. It is mostly because the UHF channels were more likely to be available in most markets. Eventually, after the digital transition is complete and TV stations no longer need to broadcast in analog, they may switch and use their current analog VHF channels for digital instead. Antennas that receive UHF stations only and ones that receive both VHF and UHF are available. If you are fairly certain you won't want to get any lower channels in the VHF 2-13 range, you could purchase one that is UHF only.
An antenna - Depending on your location relative to the stations you want to watch, a set of rabbit ears might do, but you might need a rooftop or attic antenna. You can buy an antenna that's specially made for digital signals, but any reliable VHF/UHF antenna will work.There is no need to buy expensive equipment to enjoy HDTV as long as your TV is HD and is connected to a reliable antenna. Like it can be appreciated in the picture above, my antenna is a VHF/UHF and I am able to receive on my LCD screen channel 8.1 and 8.2 in high definition.