On your right, you'll see the new 'Random posts' widget. I'm sure you can guess what it does. I got it from here. My old blog, Diary of an amateur vampirologist, used a random posts function called LinkWithin, which shared 'related posts'.
I would've used it here, too, but as my posts are generally shorter, they'd be a bit of an eyesore on the page. However, if they had a 'list' function rather than 'thumbnail' display, I woulda used that instead.