Apple's Limited Warranty http://www.apple.com/legal/warranty/ for iPad excludes coverage for damage resulting from accident, disassembly, unauthorized service and unauthorized modifications.
Apple will provide a replacement iPad for:
iPad model Out-of-Warranty Service Fee New iPad $299 iPad 2, iPad $249
Make a Genius Bar Reservation
You can get the glass replaced at 3rd party repair sources for less $, however, the Apple warranty will be voided.
iPad Repair & Screen Replacement Services
RepairZoom iPad Repair