My favorite is Blue Horse Kona Coffee.
Code:
http://www.bluehorsekona.com/home.html
It's very reasonably priced and they have free shipping, great company. If you want the true Kona experience, avoid the term "Kona Blend" and look for 100% Kona. It's more expensive, but you'll definately notice the difference. Also, try the 100% Peaberry Kona from Blue Horse, flippin delicious but pricey. Worth having at least one time though. As far as the darkness of the roast, it's strictly preference, but I prefer medium.
Good Luck!