I would highly recommend the "Border Workbook" by Janet Kime. YOu can get a used copy of the first edition from amazon for the price of a magazine:
http://www.amazon.com/The-Border-Wor...order+workbook
She has lots of borders to choose from and a whole section on how to fit a pieced border to your quilt.
Basically, you pick out your border figure out how large the border will be, then add an inner border sized to make the pieced border fit. The orginal version of the book has B&W diagrams with color photos, the newer version is identical except the diagrams are color and the price ;-)