Libertarians for Life has a fine website that includes Doris Gordon's masterpiece, "Abortion and Rights: Applying Libertarian Principles Correctly." This is the best philosophical article on abortion that I've ever seen. It's very clearly written and avoids technical jargon.
Also on the site is Dr. Paul's 1981 article--brief but strong--"Being Pro-Life Is Necessary to Defend Liberty."
The link is: www.l4l.org/library.