Carol Martin-Sperry's Good Sex, Bad Sex, No Sex - A Guide for Grown-Ups is free on Kindle today.
I read the first one and it was very useful. This one is more for my generation I think. It covers how to keep sex going after kids etc - ie the sort of thing most of us have to worry about these days!
You can find it on Amazon.
www.amazon.co.uk/Good-Sex-Bad-Grown-Ups-ebook/dp/B008DGNYUG/ref=sr_1_2?s=digital-text&ie=UTF8&qid=1340784992&sr=1-2