Wikipedia has a great list of cognitive biases. A cognitive bias is a distortion in how humans perceive reality. A lot of them are generally known, like confirmation bias (the search for or interpretation of information that confirms one's beliefs) or false consensus bias (the tendency for people to overestimate the degree to which others agree with them).
There are a few in there, however, that surprised me like the Zeigarnik effect, the tendency for people to remember uncompleted or interrupted tasks better than completed ones. That's just weird. Check it out for an interesting look at human behaviour.