Don't know if it's my most common or not, but one that I've, thankfully, caught several times before replying to customers is acocunt (should be account).
My most common type relates to the shift key. When I am trying to type a capital letter in front of a word I tend to miss it or somehow how the caps lock. So sometimes it ends up like this (aLL).
down instead of done, and vice versa. Also, hitting enter when I'm trying to do an apostrophe. I also find myself typing approbal instead of approval a lot.