this is the cheapest, easiest nic nac shelf you can find. here's what you need:
a yard stick- you should be able to find one at your local hardware store for under a dollar. you can paint it if you like, I left mine in it's natural state.
cut 3 pieces of ribbon all the same length. I made mine about 9 inches long.
fold one ribbon into a circle, overlapping the ends. put the end pointing up on the inside.
put a thumbtack through both ends from the inside. stick it in the wall.
repeat with the other two ribbons, one for each end of the yard stick and one in the middle.
slide the yard stick through the ribbons. you can glue it underneath if you want.
voila! you're done. here's mine: