Lexar and Kingston also make great CF cards. I had one 4GB Sandisk Ultra III CF card malfunction within 3 months of purchase. The problem is that when it was filled with about 1GB of data, it would freeze and not accept more. The usual reformatting and using Lexar's Rescue software didn't work, so I got a return authorization from Sandisk. Sandisk agreed that the card was defective and sent me a brand new one.
Personally, I would buy a CF card from any one of these three manufacturers. Price would be the deciding factor. Sandisk makes good cards, I just had a bad one. I don't think that Sandisk makes a better product than the other two companies, they are all equally good.