Do you stay home, in bed, avoiding ladders and black cats and broken mirrors on Friday the 13th? A lot of people dread the day, so I went looking for the reasons why.
Start where there's lots of strange, the Urban Legends page on the topic. Actually some pretty scholarly research here, tracing back to what could be the first Friday the 13th, when a French king arrested some important knights to raise tax money. Or back further... claiming the Last Supper was on Friday the 13th. Lots of text here, no pictures, but interesting stories, and more Friday and 13 superstitions.
There's another, more colorful page with similar info, including some actual medical research about the fear of the 13th, and why some think they can prove it's a good idea to stay home.
Salon Magazine did a little research as well, talking to college professors and historians, sort of summarizing others opinions on the topic.