Sometimes finding a design idea is as simple as looking in your closet. Fair Isle sweaters have great patterns.
They may look complicated, but each row only has 2 colors.
There are simple geometric patterns and not so simple geometric patterns.
These designs can be easily adapted to cross-stitch for borders and to fill an area. Start with a simple zig-zag, line or cross. Vary the colors. Add dots, circles and other shapes. Sometimes you'll be amazed at the patterns you can make with only a few colors and a few shapes.
I've even used these sweaters as an inspiration for a beaded amulet bag. It's done in peyote stitch. The grid is a different shape than cross-stitch but it lends itself to similar patterns. As in Fair Isle, each row only has 2 colors.