My newest addiction is found at http://www.sporcle.com/. There is a plethora of subjects to quiz your skills. I generally lean towards the trivia on sports. Unfortunately there are a lot of topics in the sports section that I have little to no info on, such as hockey, soccer, Olympic events just to name a few.
The one quiz that I take regularly is the quiz on Naming the Presidents. You have 10 minutes to name all the presidents. You type in a name (spelling counts) and it puts it in the order for you, which is helpful. I don't know why I am so addicted to this one in particular. Maybe someday it will come in handy...but probably not. I did learn from doing that quiz that four presidents have been assassinated, not just two.
So if you like trivia, or are bored, check out sporcle.com.