David's Tip of the Day: Summary of Keys used at BluesHarmonica.com

Harmonicas come in all twelve keys. To play in a given key you simply grab the appropriate harmonica and away you go. Each harmonica is approached the same—same blows, draws, bends and techniques—the harmonica does the key change for you. We start with the A Harmonica because it’s the most common harmonica used in blues. The common keys of harmonica are G, A, Bb, C, D and F. To learn this instrument and play along with the majority of your blues music selections, you’ll need these keys. You can purchase these as you need them in your studies, or purchase them now so you have all the keys covered.

I recommend the Hohner Crossover (~$85) or the Hohner Special 20 (~$40) for those on a budget.

Best wishes on your studies!