Which direction should the arrows point in a sorted table?

I've always went with the following:

• Ascending -- Arrow pointing up
• Descending -- Arrow pointing down

In my opinion, the visual representation of the arrow pointing up/down most accurately explains the sort order.

I don't think of them as arrows, but as a visual mnemonic of the current state. So, showing a triangle pointing down shows descending order. It is visually in line with the icon with the largest item (base of the triangle) at the top of the list and the smallest (point of the triangle) at the bottom.