We have (for only a short time longer) a 24/7 commercial free blues station. Unfortunately, they are an automated station, but even as such, was turned onto many great artists. this station was just temporarily filling a frequency, and will soon be a new format.
The experience with this station has led me to the world of sattelite radio. They have channels dedicated to genres such as blues, jazz, etc. The sattelite radio also provides info like the name of the artist, song, and sometimes album/year. That is a great way to learn about blues if you can swing it.