A few of my friends use the $20 Phillips antenna you can get at Target. I'm using a Radio Shack model that was ~$30. Honestly the best results I've seen were just using a cheap fm antenna. The kind supplied with most recievers that has two wires you pin to the wall on one end and a push on coax attachment at the other end. Don't believe anyone who says you cant get a digital signal with those. I've used it and got ~35 channels, all digital. I just finally went for one with a signal boost because I'm in a basement apartment and would loose certain channels when the weather was bad. (BTW, I get the exact same channels with or without the powered 'hdtv' antenna)
I agree with Jack Hammer to the extent that you should try the simple cheap antennnas first. Often rabbit ears do the job. They should be able to receive UHF signals (channels 14-69) because that is where most digital TV broadcasts are. A simple FM folded dipole wire antenna may work OK if you are close enought to strong signals, but it is not designed to pick up UHF channels.
The problem is that TV reception varies considerably depending on the distance from your home to the broadcast tower, your elevation, and the local terrain around your home. For example, you might be on a hillside that blocks reception. Tall buildings and trees also can have an effect. So, a one size fits all type of answer for an antenna can be misleading. Too much depends on your own local situation.
For myself, I've had very good results with a
Wineguard Squareshooter SS-1000 antenna. It's small (about the same size as a satellite dish) and can mounted almost anywhere. I put mine in my attic and installed a rotor so I can pickup both Washington, DC and Baltimore signals.
Try to avoid using the powered or amplified antennas if you can. They can be trouble, but sometimes you need them.
