AHR, you've inspired me to reveal my secret to low-fat yet creamy mashed potatoes: white beans.
With cooked white beans (if they're canned, you better rinse 'em good) and put them through a food mill. Food processer just gums them up, like it does to spuds.
The beans will come out airy and creamy. Add them to mashed potatoes, in lieu of cream. I add a dash of fat free milk and maybe one tablespoon of butter.
On the other, chubby hand, probably my favorite mashed are made with roasted garlic that gets smooshed up with some chopped asiago cheese and a little salt. Phew.