I tend to start one and finish it (I've only been quilting since August) until recently. I had started a quilt top and finished the top only to find out I didn't have enough batting and I wanted to hand quilt it. The only problem was, I've never hand quilted anything before. So I made a smaller quilt that would fit with the piece of batting I have and practiced on that one. So, still don't have batting and the sewing machine needle has broken so now I'm hand piecing a quilt. That and I'm quilting one for my mom. So I currently have 3 going unless you count the circle jean quilt I started cutting pieces for and realized I didn't have enough so stuffed it in a bag knowing I'd like to finish it one day.
But jump around if you want! You could always make a sampler like others are suggesting, or if the colors work together, you could do one like this one
http://www.quiltingboard.com/t-132966-1.htm
then you don't have to worry about sashing, just make sure they're all the same size