I'm a mutt, too.  I think my largest ethnicity percentages are English and Irish, but I'm also Welsh, Dutch, Scottish, Croatian (my last name is actually Croatian, I guess), Cherokee Indian, and a bunch of other stuff.  My dad's very into history and spent a lot of time making a family tree, and a long list of my ancestors' countries of origin.  I haven't seen that since middle school, though.  I should look for it next time I'm at home.