Hi Steven, what you're looking for are "bottom-up" shades, which use a tension system to keep shades taut when opened. Manufacturer Hunter Douglas offers their own line of Nysan Bottom-Up Shades. Blindsgalore also offers a bottom-up feature for their selection of roller shades. A couple of other great tips about this topic from a past AT San Francisco reader question offers additional resources:
A custom shade shop will do this roller shade that is mounted at the bottom of you window. The bar at the end of the shade will be of wood (slid into a pocket)which has an eye hook on it. Then at the jambs of the window there will be some hooks, say at the mid point of the window and maybe higher or lower depending on your preference. The eye hook will slide over the jamb hook at what ever heights you desire. This is not a cheap solution, because of the custom shade shops involvement. About $250.00 a window. But, no unsightly pulleys. And the shop will modify the roller mechanism so that there is constant "retraction" to keep the shade tight.