Nothing is more frustrating than a broken zipper. We have all had them on jackets for sweatshirts. You want to wear the item but you cant with a broken zipper. You take it in for repair and often the cost to put on a new zipper is more than the article of clothing is worth. Well that may not be the case with luggage. The higher cost of the luggage to often times makes it worth repairing rather than replacing.
There are several types of zipper fix it kits available if you want to try to fix it yourself.
Ebay has a great tutorial on how to repair broken luggage zipper.
Yelp has some great reviews for shops that can repair zippers in most cities around the US:
Zipper Repair San Francisco
There are even lots of videos on youtube that explain the process of fixing a zipper.