They're a little hidden amidst the pastels and cartoon characters, but we found a few simple and modern blankets at Walmart that might even make be good starting points for choosing your colors or the tone of the room. The above is the Sumersault -Lollyland. It coordinates with a set of bedding, mobile, valance, and rug.
This one, Blooming Delight, also by Sumersault, also coordinates with matching items.
Perhaps not quite modern, but this white hand-stitched quilt by George is also one of our picks.