Thickening agent other than corn starch or regular flour?

What is it that you're thickening? And how much of it is there? Arrowroot will keep a liquid clear (good for fruit glazes etc) but if it's something savoury and you're not too worried about texture then even some potato would thicken things up... If a gravy is too thin then a dash of cream will add some body to it....

Depends on the application. Butter can be, also potato starch, arrowroot, tapioca, blood, beans/lentils.