All credit card numbers contain a 6 digit prefix, the prefix is the sequence of digits at the beginning of the number that determine the credit card network to which the number belongs. The first 6 digits of the credit card number are known as the Bank Identification Number (BIN). These identify the institution that issued the card to the card holder. The rest of the number is allocated by the issuer.
Bank Identification Numbers, BINs are generally considered sensitive information and is normally provided by merchant service providers, who normally are able to supply monthly updated BIN number range tables for all cards (Visa, MasterCard etc.) except for AMEX, Diners, JCB and Discover.
But there exists public available BIN number databases on the internet.
Mars Banks Base - a database with MasterCard bank identification numbers (17,297 records), VISA bank identification numbers (35,154 records), American Express bank identification numbers (1,215 records).
Dumpz.biz Binlist - a collection of rather old databases of BIN numbers.
Wikipedia - List of Bank Identification Numbers - Wikipedia's collection BIN numbers.
The databases from 'mars soft' and Dumpz.biz seem to contain some old data.