I've discovered that, if I want to a) keep my job, and b) maintain any level of productivity, I have to stay away from these sites at all times while at the office. These can easily knock out 2-3 hours of my day.
Dispatches From the Island, a blog by Jorge Garcia (Hurley). Just discovered this one the other day (h/t to Shan), and immediately killed about three straight hours going through the archives. This is mainly just a bunch of random stuff that he comes across or thinks of, but every once in a while you'll get some pretty cool behind-the-scenes Lost stuff as well. Mainly, he's just a funny, self-deprecating guy. And he likes fart jokes. Bonus.
The Fug Girls. I know absolutely NOTHING about fashion. In fact, my fashion sense seems to be stuck somewhere around 1997...lots of plaids and Dockers in my closet. And yet, this site never stops cracking me up, plus there's a fair amount of eye candy, as well.
Ugly Baseball Cards. This one isn't updated as often, but every time it is, it's Gold, Jerry! Gold!.