Have you heard of zenback? It's currently the hottest related posts widget from Six Apart currently provided to Japanese bloggers only as beta program.

It's lightweight (loads fast), fetches Twitter mentions (similar to BackType), Hatena bookmarks, mixi check, and recently added Evernote button. Options (i.e. how many related items to show) are configurable, you can also show referers to your posts.

One interesting (zenback's main) feature is it automatically shows related posts from other bloggers who use zenback. So for example, your posts may be liked from A-list bloggers even if your blog is normally getting 30 visits a day (like my Japanese blog...).

In English there're several related posts widgets for many types of blog platforms. For example, LinkWithin is quite popular for almost any types of blogs, and there're great plugins for WordPress, too.

Since Blogger doesn't offer related posts feature (I miss WordPress for this), I've been hoping Six Apart teams in Japan would make zenback global. Once it's available to anyone in various languages, I'm sure most bloggers will love it, perhaps better than BackType.

You can see live example from my Japanese blogs (recommended for Japanese readers).

For those who aren't familiar with Japanese online services. Hatena Bookmarks is Japan's largest social bookmarking service, and is still powerful and influential for bloggers. Mixi Check (developer document in Japanese) is just the same as Facebook Like. Evernote.... I don't think I need to explain that. ;)