I just got some 4 pocket pages today. While I liked the ones made by Ultra Pro that was mentioned earlier, I decided to go with a different brand called Fageverld. I really liked the feel of their pages, and their quality. I can easily move them, similar to 9 pocket pages. They can house PSA and BGS cards, and a few others.
The thing I don't like about them though is that the backside of the pages are not as clear, compared to the frontside. I don't know why they manufactured it like this. The backside and frontside should be the same in clarity, so collectors can easily read the back. Anyways, I'm not too concerned about it. Another thing I don't like is that they don't accomodate SGC cards.