simpletech is a very good brand for the ax, I (i dont have one but) have heard that panasonic is also good. Hope that helps. I would recommend a 256, plenty of space for me. I know they have 512 cards and are working on a gig but I don't watch movies or listen to mp3 on my ax so I don't need that. If you are interested in movies or mp3's then get a larger one or a couple of 256's. they fill up fast like that.
Edit: Howard2k Love that quote!!:D ;)