There are lots of mix-in choices available for brownies besides chocolate chips. Nuts are the obvious choice (especially walnuts or pecans). Other types of chips are great also. Think: mint chips, butterscotch chips, peanut butter chips, or toffee bits. And don't forget dried fruit like raisins and dried cranberries. The only caveat is to limit the total amount of mix-ins to no more than 2 cups.