From my personal experience, printing gift certificates online is simple, just choose, add information, and order. Here is one link of a reputed online printing company: http://www.artdigitaltech.com/, for your preference.
For the easiest ordering process with the best quality prints you should definitely check out www.redtagprintsale.com -- Everything you'd ever want for business promotion with the ease of mind and time so you can focus on your business.
well there are online places that do a credit card type of gift certificate.
or this one: http://www.theplasticcardfactory.com/index.php
---He who gets greedy like a pig, gets slaughtered like a hog!