My usual is leek and potato which I do by boiling potato and leek (funny, that) with minimum stock and a little butter, then blending it, adding milk if it's too thick.
Last week I tried one I learned at work - you roast a sweet potato, red peppers and red onion for about 40mins, then blend it with stock.
I am now working full time and doing a hot lunch so I would love some more very very VERY simple ideas.
:)