American Express offers their logo, as well as a number of images that combine their logo with that of other credit cards companies' logos:
Discover offers individual images of each of the credit card companies logos in different sizes:
Diners Club offers an array of Payment Option, Sponsorship, Card Art and Tagline images in multiple resolutions and formats including GIF and PostScript:
JCB offers one image for each of the card types that they offer:
