I was recently directed to Hive account@danielsaori who runs a comment contest. He'll pick out a post from a relatively new user and send people to read it and formulate a comment which hopefully would intrigue the reader enough to go and look at the commenters blog. To enter, the comment needs to actually be posted on Daniel's contest post, but it can be quoted from the comment left on the actual post, which I think is preferable.

I don't know if this is something you think worth adding to the list.