Something like this:

Maybe minimal and simpler

It seems one of the standard these days is

There is another one that doesn’t even require you to log in. It just sees you as being logged into your facebook account on the browser and inserts the box at the bottom should you wish to comment. I can link to a specific blog that does it, but i’d rather not do it while i’m here at work.

It’s one of these, I used it a while back