When they think of the incarnation, many [Evangelical] students initially think of Mary as a kind of vessel for the life of the Son. They reduce the issue to that of a “rent-a-womb” lease. However, this quickly dissolves once they begin to come to terms with a real incarnation in which the eternal Son of God assumes real human nature in the womb of Mary. At that point, the debate about Mary as Theotokos catches fire and the race is on to come to terms with the early christological debates. (From the Forward to Mary for Evangelicals by Tim Perry)
Finally, Evangelicals are waking up to the Blessed Virgin and her importance. I recommend Tim Perry's book to any non-Catholic readers who want a Sola Scriptura portrait of Mary.
Another book that can help Evangelicals understand Mary is The Real Mary by Scot McKnight. After introducing you to the "Biblical" Mary, he does a fair job explaining what Catholics and Orthodox believe and why.
I especially liked his declaration that it is okay for Evangelicals to call Mary Theotokos, or Mother of God:
We Protestants can, and rightfully should, stand with the whole Church on the importance of what the Council of Ephesus decided. If "Mother of God" means "God-bearer" as the one who gave birth to the human Jesus who, as a single person was the God-man, then we can also stand together with Roman Catholics in affirming Mary as the "Mother of God".
McKnight also says it is alright to conclude that Mary was Ever-Virgin (Martin Luther and John Calvin agreed) :
What perpetual virginity teaches about Mary is that her task was so holy and her womb was so sanctified by the grace of God that Joseph concluded, out of reverence for what God had done, that he simply would not 'invade' what was holy.
As Mary herself prophesied, all generations will call her blessed--I don't think she meant just Catholics, Eastern Orthodox, and a few Anglicans!