You might also like noticed on some site there is some featured posts in post-footer with its links and titles you might also like, these are the related posts.There are many ways to add that widget in your blog,Here is some useful tip to place widget for your blog,
1.linkwithin: Linkwithin is a website that can install you a free related post widget for your blog, it's quite easiest and nice.Details in how to setup / install linkwithin,
2. Outbrain: Outbrain is a another nice website which can create related post for you, but this site requires a registration, but after reg. you can use it in many various platforms like blogger, wordpress and many more.
Outbrain also provides analytics for your blog,so this is a better option to use this website.
3. nRelate: nRelate Provides widgets for both registered and nonregistered users of this site. It has a style option , there you can choose different styles for your widget.
So after reviewing all threes you can choose any one of them. nRelate comes with default text you might also like!! and you can customize it.