I was working on a shopping cart UI recently, and I was shocked by the dearth of hi-res credit card logos out there. Not only that, but there are a lot of previous brand logos kicking around out there. You think with all the e-commerce going on, the credit card companies would want to go out of their way to provide high-quality, up-to-date images of their brands. Not so. I could find nothing of the sort on any of the credit card web sites. So I created my own.I started with the largest logos I could find (Tin Eye was a great image search tool for this), then used Photoshop to remove the compression artifacts and correct the colors. The Amex logo was impossible to fix, so I ended up recreating it in vector form in Illustrator, then applied the blue gradient in Photoshop.
Here is a ZIP archive containing all four high-res credit card logos. Enjoy. If you like them, link back to this page from your blog, Delicious, Digg, or wherever.

Nice job! I like your simplification of the Discover and Visa logos.
P.S. Your captcha doesn't work in Opera 9.5 on OS X.
I can't take credit for the designs. Those are the updated logos for those brands. Check out http://visa.com and http://www.discovercard.com/
Thanks! Used the logos on a mass post mailing to our 2500 customers