On the right-hand column of every diary, there is a "recommend this diary" button. If you think the diary is a particularly good one, click the button.
Those diaries with the most recommendations now show up in the new "recommended diaries" box. New recommendations are weighed more heavily than those a day or two old.
This is new code, so report any bugs. Also, we're open to tweaks that would make it work better, if warranted.
Update: Hmmm, I've already found a couple of bugs. This'll need some additional tweaking.
Update 2: Most of the bugs seem to have been worked out. Also note that only registered users can recommend diaries.
I get nothing from people registering, but the user experience is like night and day if you do register. Just the ability to see what comments you've read and which are new are worth the price of admission (which is $0).