HI, Are you talking about a border around the whole quilt or sashing around each individual block -
If you are talking about a border - I would recommend auditioning fabrics at your local quilt shop - take the quilt and go there - put it down on different fabrics and talk to the workers - they will help
If you are talking about sashing - I would look at the fabrics you have used in each block and get a fabric that complements them - sometimes a darker solid fabric works well as it wil send your eyes in from the sashing to the block itself.
Again, you could take the blocks to the quilt shop and the workers again will help you and you can audition fabrics till something just talks to you.
Good luck
Althea