Sony themselves only make an 8MB card. If you want bigger, you have to go third-party, and you run the risk of losing data. A lot of people think that "one memory card is as good as another", but that's not the case. Third-party memory cards are notoriously unreliable and prone to catastrophic failure or corruption of the files on it. For every person you see who loves them and swears by them, there's another person who lost all of his game saves on one.
Me, I use only Sony memory cards. In fact, I only use Sony peripherals period. The only non-Sony peripheral I have is my DFP, but that was designed hand-in-hand with Sony, probably the only peripheral that's not only licensed, but endorsed by Sony.
Oh, and I have a MAXDrive. Which recently deleted about half of my game-saves, so I can't give that a glowing review.