One of my favorite "time-filler" sites is MentalFloss.com

They also have great t-shirts (though over $15 for a t-shirt seems really expensive to me, so I'll probably never buy one.

As a math major, I have to love this one:

I wish I actually had the nerve to wear this one, it cracks me up:

I really like both the design and execution of this one:

There are tons more here, I have to run to (another) firm party!