CommentLuv, a plugin which allows folks who graciously comment on your blog to enhance their own blog's profile by adding a link to their most recent blog post at the end of their comment. In other words, it allows bloggers to "share the love" by offering something in return for comments. A win win.
For a long time it was only available to bloggers using the WordPress platform, a big frustration for those who are using the Blogger platform.
Once you have it set up, your Comments box can look like this: