My first quilt that was just "mine" was just larger than a double, but could be used on a queen. I wasn't into much accuracy then, since I was a teenager.
http://www.quiltingboard.com/t-8956-1.htm
My daughter loves this quilt and put it in her guest room!! Guess I'll have to make her another one that isn't quilt so awful.
But if I am just making a quilt for fun, it almost always is a queen. It seems to be the most versitle size. Well, except for baby quilts. Guess I need some twin size on hand too.. . .