I can recommend the Winegard unit I have. They have higher gain models available, like the AP4800. These are UHF only but they do pass VHF (with some mild attenuation). I hear good things about the Channelmaster 7777 too.

I bought the Winegard because an acquaintance whom used to install many TV antennas in Northern Ontario recommended it. It was sound advice. It doesn't have to go right at the antenna. It'll work best there to be sure, but like I mentioned mine is in the basement and definitely improves things.