Image property of sew4home.com
Here is a tutorial over at sew4home for some pretty valances with a lace inset. They also put a few rows of decorative stitching on them, but if your machine doesn't have decorative stitches, this is optional. The valances would still be very nice without them. If you do have decorative stitches on your machine and you haven't tried them out, this might the project to use one of them. :-) You could also sew on ribbon instead.
Home made valances and curtains can add a lot of color or personality to a room since you can use fabrics that would never be used in pre-manufactured types. I've made quite a few over the years. Some for myself, but also some for my siblings. In a room where there are Venetian blinds, and cheerful valance can really make in look more cheerful and homey (homely - of you're British).