Did reformation leaders throw out the Summa Theologica? St. Thomas Aquinas's seminal work the Summa Theologica was an attempt to catalog all the theological arguments ever conceived. 

Much of the reasoning is rooted in the Natural Law and it's what Catholics believe today. It's the reason we've got such strong opinions on abortion, birth control, embryonic stem cell research, homosexual "marriage" and more even though private interpretation of the Bible could potentially lead one to believe otherwise.

What I wonder, is how much of a common ground is the Natural Law (specifically as it relates to the Summa) and how did the reformers (Luther, Calvin, Wesley, etc.) decide whether or not to accept it?
I can only speak for Calvin. AFAIK, he never explicitly interacts with Aquinas or the Summa. In Institutes he does reference "The Schoolmen" many times, but he seems to have in mind mostly later-medieval theologians rather than the angelic doctor himself. That's a shame, because Aquinas would have been a much more worthy opponent.

Protestants in general tend to be skeptical of natural-law arguments. Calvin himself believed that our only reliable knowledge about God comes from special revelation and he is very hard on the "Papists" for making stuff up (i.e., the incredible detail some writers claim to know about the kinds and hierarchies of the angels).

That said, I believe Calvin would have come down on the same side as the Catholic Church on the issues you mentioned. He certainly would have opposed contraception.

Edit

Here are a few google results, suggesting that Calvin probably did not have access to the Summa: 

Calvin on Aquinas

Luther, Calvin and Aquinas: On Grace