I often trundle through Wikipedia looking for trivial minutiae about my favourite TV shows, video games, and fictional characters in general. Lots of great material there.
Then I look at the articles on historical combat and am occasionally forced to laugh (like when the article on ninja claimed that real-life ninja used to have magical shoes that allowed them to run on water).

However, the single greatest article on Wikipedia is probably the one on Hammerspace. It's awfully amusing, as is its discussion page. It's articles like that which contribute to the fact that Wikipedia will never be taken seriously as an academic resource, but it's those very articles that make it such an awesome site.