I came across this article via reddit.com
13 things that do not make sense
What strikes me about this list is that for all that we believe we understand and have figured out, there still big enough gaps remaining in our knowledge that we may discover that we really don't have things so figured out.
What will they look back on in 100 or 500 years and say, "I can't believe they thought (insert current scientific knowledge here). What were they thinking? Those ignorant slobs!"