I have owned the VRFM8B for 8 months or so. I bought it from Costco for 24.99. This thing works great. I use it everyday in my 60 mile roundtrip to work. The model I have is the VRFM8.
There are 8 channels to pick from. Four at the lower end and 4 at the upper end of the FM band. Just pick the one that has no broadcast on it and set your FM radio to that frequency. There is also a 3 ft audio cable that lets you connect your iPod or other hard drive MP3 device to the modulator.
Here is a link to the company's website for these FM Modulators.
Roadmaster FM Modulators
edit:
I would like to mention that Walmart is selling the VRFM7, which is the second generation of this device. I have the VRFM8B and there is also a newer VRFM9 which I have yet to see. I have also seen the VRFM7 for sale at Target.