Cover Flow looks cool, but I find it to be quite impractical a lot of the time. Useful for images etc., though.
List view is great when there's loads of items to look through. I hardly ever use column view anymore now that Leopard has the Path Bar feature. It seems to be the standard for file saving dialogues, though.
I LOVE how in Leopard you can change the grid spacing in Icon view, though. Icon is definitely my favourite view. 🙂