I'm using a 1GB SD card bought from eastgear.com, I think it's the NCP highspeed (which I also think is a rebadged panasonic), high speed anyway. Works fine, I had it in vfat, it worked in my tre600, then I stuck it into my c760 and reformatted as ext2.
aside - I bought it for SGD$299, and a few months later they were selling it at COMEX 2004 for SGD$255. sigh.