www.discovercard.com
*Discover Platinum Gas, Home Improvement, Restaurant and Education Cardmembers, certain Gold Cardmembers and Miles Cardmembers are not eligible to participate in this promotion.
Remember, you don't get any support for purchase issues from Discover. Any issues will have to be settled by yourself, with no assistance from the company, unlike other credit cards.
EDIT: UNTRUE (by didyousearch)
DISCOVER HAS BEEN COMPLETELY HELPFUL!!! I do not agree with the above statement (by Juliet12783)
Edit: Do not quote me, but I think a common theme I've seen with people who had trouble disputing a transaction with Discover, if the transaction was swiped like a gas station or restaurant, Discover tended to accept the merchant at face value. Of course, what we never hear is was the dispute filed in writing, was the initial response responded to with a well written letter. Phone calls never preserve your rights and once the 60 days are passed, Discover won't look back (unless outright fraud was involved). (by gatzdon)
Discover card will instantly credit your account and then begin investigation if you call in with a dispute.