The Botkier Sasha Duffle fits your specs. Can be carried over the shoulder as a hobo or on the arm or by hand as a duffle. It seems like it can be stuffed to carry a lot, but when it's not stuffed, it contracts and looks very stylish.
It comes in black and pudding (tannish). Miostyle says it will come in chocolate. NM's used to sell it -- also Active Endeavors and Shopbop.
The third photo below is Cyclgrl from this forum. She uses it for work and travel, and puts her laptop in it.