I use this Philips antenna
in my spare room with a digital OTA converter box and it works great. I haven't tried it with my TiVoHD yet, but I plan on doing so in a couple of weeks when I drop my cable subscription (recently got U-verse).
I bought it for around $15 at Target, with many online retailers selling it for much less, but I wanted to be able to return it hassle-free just in case I needed something more sensitive.
I'm in the foothills of LA, close to Mt. Wilson which has numerous TV antennas on it. Your performance will vary depending on what obstacles are between you and where the antennas are in Chicago.