You can search Ravelry by the amount and type of yarn you have and the craft you want to do. See what comes up.
I would go for a ripple blanket with 6 different colour but it probably isn't enough as CatCushion says. I am doing a granny stripe and I am on my third ball of 100g Stylecraft Special DK and it will just about single bed sized when finished. About 1500g as there are 5 colours just as an idea of what it takes.