@lewisandrew, are you looking for resources for yourself or others? The books that have helped me the most aren’t specifically for singles. Anything that opens my eyes to the needs around me and equips me to meet those needs will cause me to spend my singleness more wisely. I love reading Christian biographies because they give me a vision of a life on fire for God.
If you’re looking for yourself, do you find yourself drawn to certain areas of ministry? I might have some ideas of books that would be particularly inspirational or helpful for your interests. I can’t think of a book for singles that I’ve liked better than Sam’s, so I can’t help much there.
Concerning Genesis 2:18, is it significant that there were no other humans on earth when God said that? Adam was alone in a way that we aren’t even if we are single. Since Paul said that it is good to remain single (1 Corinthians 7:8), we can’t use Genesis 2:18 as a blanket statement that it’s not good to be single.
I also wouldn’t work at desiring marriage. Since God is currently leading me to be single, I should strive to be content in that rather than trying to desire the thing He said no to. I need to be sensitive to His leading so that I don’t let things like my career get in the way of marriage. But as long as I’m loving God with my whole heart, I’ll know if He is leading me in a new direction.
Psalm 73:25-26 says it best: “Whom have I in heaven but you? And there is nothing on earth that I desire besides you. My flesh and my heart may fail, but God is the strength of my heart and my portion forever.”