So many good suggestions here. The first thought that came to me is applique vine and flowers and leaves with maybe a butterfly, bird or kitty thrown in. Here is a blog I just found with lots of pretty applique that could easily be incorporated into a border, like the vine coming out of the basket with the little heart flowers or scroll down to the pineapple quilt. Lots of ideas and eye candy for applique
http://www.therabbitfactory.com/blog/
But being a LAQ I always like to consider enhancing a quilt with the quilting. Have you decided how you are going to quilt it? A plain border can be a stunning canvas for some pretty girlie quilting that won't over power it. If you quilt some sort of floral or feathery motif in the white squares you can carry that out into the border as well.