[sdqali]

I wrote Commentary to address this issue - https://github.com/sdqali/commentary

[eksith]

Now this looks interesting. Integration looks pretty simple since it's a JS include via jQuery. Would you happen to have any running demos somewhere or perhaps some screenshots?

[jeena]

Would be cool if you had some screenshots up there.

[pvorb]

This looks nice. I'll probably try it, if I can persuade myself to install Ruby.