What most surprises Caesar when he is attacked? What might Caesar have been thinking as he died?

"Et tu, Brute?  Then fall, Caesar."

Caesar mentioned his concerns about guys like Cassius way back in Act One.  Remember how he wished Cassius was "fatter"?  So it's likely that he wasn't too shocked to see Cassius and some of the others attack his leadership, but he never expected it from Brutus.  Brutus is a well respected leader in Rome, and, more important, a very good friend to Caesar.  When you're being attacked, you expect your friends to help you, not join the fray.

What was he thinking as he died?  Tough to say.  I'd like to think the last thing that went through his head was about how famous these eight guys will be because they've killed the mighty Caesar!  In reality, he was probably wondering what he did wrong to deserve this.  Remember that only a month ago he was returning to Rome as the hero that defeated Pompey; now he's being stabbed in front of everyone.  I'm sure he was quite confused about the inclusion of Brutus as well.  Ultimately, he was probably upset about never getting the chance to wear that crown.