Test numbers from Authorize.net:

370000000000002 - American Express Test Card

6011000000000012 - Discover Test Card

5424000000000015 - MasterCard? Test Card

4007000000027 - Visa Test Card

4012888818888 - Visa Test Card II

3088000000000017 - JCB Test Card (Use expiration date 0905)

38000000000006 - Diners Club/Carte Blanche Test (Use expiration date 0905)