Olive Tree software is another choice. They have a free reader which includes the KJV and MH Concise Commentary. They are stored on the iphone/ipod, so you do not need an internet connection. They also have some free modules and some for purchase.
Olive Tree

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Chris
Teaching Elder (PCUSA)
West Virginia
"Although the fig tree shall not blossom, neither shall fruit be in the vines; the labour of the olive shall fail, and the fields shall yield no meat; the flock shall be cut off from the fold, and there shall be no herd in the stalls: Yet I will rejoice in the LORD, I will joy in the God of my salvation." (Habakkuk 3:17-18)